Contrary Direction Research Articles

III. The resistance of electrolytes to the passage of very rapidly alternating currents, with some investigations on the times of vibration of electrical systems

The electromagnetic effect of the currents induced in a conducting plate by alternations in a primary electromagnetic system in its neighbourhood, is, at a point on the side of the plate opposite to the primary system, in the contrary direction to the electromagnetic effect of the primary. Such a plate, therefore, tends to shield off from a secondary system the induction due to the primary, the diminution it produces in the current induced in the secondary depending upon the conductivity and thickness of the plate and the rate of reversal of the primary current. If the rate of reversal is infinitely rapid, a thin plate of very badly conducting substance will be sufficient to screen off from the secondary circuit all the induction arising from the primary, while, if the rate is very slow, a thick plate of the best conducting metal will hardly be sufficient to do this.

Mangrove as a Destructive Agent

As I have never seen the mangrove mentioned but as a conservative or productive agent as regards geological change, it may be interesting to readers of NATURE to hear of its acting in a contrary direction.

Societies and Academies

PARISAcademy of Sciences, October 20.—M. Daubreé in the chair.—The following papers were read:—Researches showing the power, the rapidity of action, and the varieties of certain inhibitory influences of the brain on itself or on the spinal cord, and of this latter centre on itself or on the brain, by M. Brown-Séquard.—Discovery of a small planet, by Mr. Peters (telegram from the Smithsonian Institution).—Observation of the planet 206, Peters, at the Paris Observatory, by MM..Henry.—Observations of declination, inclination, and horizontal intensity in the basin of the Mediterranean, by M. de Bernardiére. These observations were made during a voyage of the training-ship, La Flore, in 1878-79. The numbers for some twenty-six places are tabulated.—On whole functions, by M. Picard.—On the Laurent saccharirneter, by M. Laurent. Two improved models were presented, giving more light and distinctness, while the reflections in the tubes are suppressed.—New researches on the mode of union of cells of the mucous bodies of Malpighi, by M. Ranvier. These cells, formed of masses of protoplasm with nuclei, are united by protoplasmic filaments, which are common to them and each of which does not result from junction of two filaments placed end to end, nor is the nodule occupying their middle the mark of a junction or juxtaposition; it is an elastic organ, which allows of easy enlargement of the spaces destined for circulation of nutritive juices between the cells.—On asphyxic glycsemia, by M. Dastre. Cl. Bernard affirmed that a prolonged asphyxic state destroyed the glycogen of the liver, and made the sugar disappear from the blood. Some physiologists hold, on the contrary, that in accordance with Lavoisier's theory, sugar accumulates in the blood when the oxygen (for its combustion) is diminished. M, Dastre considers we must distinguish between the effects of rapid asphyxia, immediately consequent on withdrawal of oxygen, and the consecutive effects of slow asphyxia (such as wasting of tissues and exhaustion of reserves). Rapid asphyxia may be realised in two ways, making an animal breathe air confined in a closed vessel, or making it breathe in rarefied air constantly renewed. He tried both on dogs, and found the quantity of sugar in the blood to vary in contrary direction to the quantity of oxygen (less oxygen, more sugar).

THE NORWEGIAN NORTH ATLANTIC EXPEDITION

THE expedition left Bergen on June 15, and proceeded without interruption to the Westfjord, in Nordland, where we had our first station. A temperature-series was here taken with Negretti and Zambra's new deep-sea thermometer, which showed 10°7 C. on the surface, a minimum of 4°4 in a depth of 40 fathoms, and 6°5 at the bottom in 340 fathoms. The Vöringen stopped some hours at Tromsö to take on board a pilot, and proceeded to the Altenfjord, where we found 7°3 at the surface, a minimum of 2°7 in a depth of 100 fathoms, and 3°9 in 220 fathoms at bottom. From Alten we went to Hammerfest, where we stayed two days. Our next stations were in the Porsangerfjord and in the Tanafjord. On all these stations we dredged and trawled with good success. On June 26 we were lying at Wardö, where Capt. Wille made magnetical observations of force and inclination. The declination was determined the day before off the coast by going round with the ship, and taking bearings of the sun on different courses. On June 27 we put to sea on an eastward course. The barometer was falling rapidly, and at midnight the wind and sea got so heavy, that the ship was put with the stem against the wind, and we were lying almost still. This situation lasted till the next night, when we again proceeded on our course, but very slowly, the ship pitching heavily, and the wind being constantly ahead. In this manner we found 0° C. at the sea bottom, in about 71° 30′ N. and 36° 30′ E. from Greenwich. We then sailed northwards and westwards, and passed the said bottom temperature several times, so that I am now able to give its situation pretty accurately in the chart. The northern part of this zero line forms a bay east of Bear (Cherry) Island, where the warmer water reaches a higher latitude, and runs close to the east side of that island, where we for the first time observed the polar ice. The temperature-series showed the accuracy of Weyprecht's observations, that the colder Polar water edges itself along the bottom from the east and north, and the warm Atlantic water runs out in a similar edge in the contrary direction towards Novaya Zemlya and Franz-Joseph Land. On July 4 we were at Bear Island, on the south-east side. We were happy to find the sky almost perfectly clear, a rather rare occurrence on this island. The ship was anchored outside the open coast, and we went on shore at the mouth of a little river, in the vicinity of which there stands a hut, which has been the abode of wintering parties. Here we deposited the mail which we brought for the Dutch polar expedition in the Wilhem Barentz schooner. The place was marked with a flag, and the letters, &c., dug down, inclosed in an outer wooden and an inner sheet-iron soldered box. I took a tour upon the nearest hills, collected some rock specimens, and measured the altitude of the highest peak on Bear Island, Mount Misery. The calculation gave me a height of 1,787 English feet, a result which I regard as very accurate. After dinner we weighed and proceeded to the south-west; crossed, the following day, the zero line of bottom temperature on the bank between Bear Island and Norway, sounded in 1,024 fathoms on July 6 in lat. 73° 6′ N., long. 11° 56′ E.; we went then east-south-eastwards, crossed again the zero temperature line, and shaped our course for Hammerfest, where we arrived on the 8th. The ship is now cleaned; we take in coal, and expect to be ready to sail on a westward cruise in three days. Our first cruise has yielded thirty-eight soundings, seventeen temperature series, ten dredgings, and seven trawlings, all successful. New species of animals have been found by our zoologists. Negretti and Zambra's newest reversible deep-sea thermometer has done us great service; the instrument has, almost without exception, worked very well. I have constantly compared its readings from the bottom with the reading of the Casella, Buchanan's improved form, and found a very close agreement. As I supposed, the wooden box which carries the thermometer gets water-soaked after a few experiments in a few hundred fathoms, so that it no longer floats, but this is no drawback, as the lead rushes down so fast that the thermometer always keeps its upright situation till it reaches the bottom, and it never requires more than three minutes for a perfect accommodiation to 0.1 of a degree. I there fore regard this instrument as a very important improvement, and feel much obliged to the inventors and makers.

Societies and Academies

BELGIUMRoyal Academy of Sciences, June 7.—M. Quetelet presented a note on the solar eclipse of May 26, 1873.—M. Montigny gave the results of a second series of experiments made on the spire of Antwerp Cathedral, in which he determined barometrically the heights at several points, in winds of different direction and velocity. His tables show a difference between the calculated height and the real height, the latter being greater for winds of the eastern semicircle, while the former is greater for westerly winds. In north and south winds, and those closely neighbouring, the heights measured both ways closely agreed. The differences between true and barometric altitude for the same gallery increase regularly, but in contrary direction, from the meridian to the azimuths east and west, when they each attain, their maximum value. The height, barometrically measured, increased, as a rule, with the velocity of the wind. No connection was demonstrable between barometric height and inclination of wind. Observations at Namur and Brussels are compared with those at Antwerp, and show a cycle like that just described, only the regions to which the maximum and minimum (barometric) altitude correspond are, at these places, in the contrary direction to those at Antwerp.—M. Melsens communicated a paper on the effect of reducing alcoholic drinks to very low temperatures. A liquor like brandy may be cooled to—60° C. without being painfully cold to a person taking it. From the phenomenon of congelation in ordinary and sparkling wines, M. Melsens seeks to show how wines and beer also may be improved by application of cold.—M. Louis Henry described researches on the etherised derivatives of alcohols and of polyatomic acids; also on propargylic compounds.—M. de Selys Longchamps made a third addition to his “Synopsis of th Gomphines,” of which he cars now enumerate 188 species(seventeen of these being new), arranged in forty-three genera and subgenera.—M. Van Beneden gave a summary account of results from a voyage to Brazil and La Plata. His main object had been to study the fauna of the American coast, and specially of Rio. He describes the frequent formation of lagoons by the deposit of a transverse bar separating the water of a bay from that of the sea. Fresh water continually entering such lagoons, their saltness disappears, and an interesting question was, how had the original ocean fauna, here enclosed, been affected by the change of physical conditicns. M. Van Beneden made various dredgings in the bay of Rio (in which the tidal change of sea-level is very small), and in these lagoons, and promises future communications on the subject. He mentions having found in some lower forms of Crustacea (Lernanthropides and Clavellinæ) a double circulatory system like that in Annelides. Besides the lacunar system, in which circulates a colourless liquid having white globules, there is a complicated system of vessels with proper walls, containing red blood without globules. There is no connection; the two liquids do not mix. The colouring matter is hæmoglobin. The branchiæ and trunk, alternately contracting and dilating, put the liquids in circulation. The author also mentions having dissected a lamantin (disinterred for his benefit), and a dolphin, and describes exceptional features in both. The paper gives several interesting zoological facts.

Sense of direction

IN Mr. Darwin's article in NATURE for last week there is a passage about “the sense of direction being sometimes suddenly disarranged,” that brought to my mind assertions I had frequently heard made when travelling some years back in the wild parts of the State of Western Virginia. It is said that even the most experienced hunters of the forest-covered mountains in that unsettled region are liable to a kind of seizure; that they may “lose their head” all at once, and become convinced that they are going in quite the contrary direction to what they had intended, and that no reasoning nor pointing out of landmarks by their companions, nor observations of the position of the sun, can overcome this feeling; it is accompanied by great nervousness and a general sense of dismay and “upset;” the nervousness comes after the seizure, and is not the cause of it. I was present in a company of hunters when a tale of this “getting turned round” was told as a good joke against one of the party—a Nimrod of renown—the leading features of which he was reluctantly obliged to confess to the truth of, while denying some minor points that had been added to embellish it, as making him more ridiculous than he was: it would take up too much of your space to tell the particulars of the story. The feeling is described as sometimes ceasing suddenly, and sometimes wearing away gradually. Would it not be strange if it should appear that there is a “sense of direction” other than an acquired sense of direction the result of unconscious observation, and that some animals possessed the first in a pre-eminent degree? The wonderful faculty hunters possess of finding their way through immense mountainous tracts so thickly wooded that one cannot see farther than a few yards at a time, may perhaps be accounted for by this power of unconscious observation alone; but is it so easy to account for a sudden derangement of the sense of direction, and the peculiar distress it occasions, even when there is no ground for alarm on the score of safety? This appears a kind of converse of the instance Mr. Darwin gives of the case of old persons losing their way.

On the probable cause of the non-existence of deposits between the Permian and the Lower Silurian in the Southern Uplands of Scotland

The great Silurian district in the south of Scotland, named by Mr Geikie ‶the southern uplands of Scotland,″ presents the phenomenon of large patches of red sandstone of Permian age superimposed in a nearly horizontal position on the almost vertical Silurian rocks. This sandstone has been entirely worn away from the hills and extensive valleys by glacial and aqueous action; in other places less exposed to erosive forces patches of it remain; while in many of the narrower glens and gorges, where it has been comparatively protected from erosion, it has been left in masses of great thickness. The enormously lengthened Devonian and Carboniferous epochs which succeeded the upheaval of the underlying rocks have left no trace of their existence in this locality. This gap can only be referred to one of two causes—<i>first,</i> either all the Devonian and Carboniferous deposits have been removed by denudation between the period of upheaval and the Permian epoch; or, <i>secondly,</i> no Devonian or Carboniferous deposits ever existed in the district. Finding that there exists no evidence of ice action, which is the great agent in denudation, between the Silurian and Permian epochs, and that even granting great denudation during this period, it is highly improbable that all traces of the intervening deposits would be entirely obliterated had they existed, the author is driven to the hypothesis that no deposits ever existed in the district in question between the Silurian and Permian; and that, during the deposition of the Upper Silurian and Old Red Sandstone in other parts of the globe, the Lower Silurian of the southern uplands were high and dry above the sea. Between this epoch and the Carboniferous, the author conjectures that the Silurian rocks were slowly sinking, until during the Upper Carboniferous period they were once more completely covered by the sea. Then commenced the deposition of the Permian sandstone, which filled all the crevices and hollows, and which may have formed a thick crust over the whole of the underlying rocks. At a later period there ensued a movement in a contrary direction, and a slow horizontal rising took place,—not a violent upheaval like the former one,—but a gradual upward movement, until the old Silurian rocks, with their accumulated crust of sandstone, once more emerged from the sea. Then ensued the glacial epoch, which has left such extensive tokens of its presence, still further wearing down the hills and scooping out the valleys, from which it has been mainly instrumental in removing the deposit of Permian sandstone, leaving it only in narrow gorges and places protected from its action.

XVIII. Electro-physiological researches. —Eleventh series. On the secondary electromotor power of nerves, and its application to the explanation of certain electrophysiological phenomena

The object of this memoir is to describe experiments which prove that whenever a nerve is traversed by an electric current, it acquires in all its points a secondary electromotor power, and consequently becomes capable of producing in a conducting homogeneous circuit, whose extremities touch any two points whatever of that nerve, an electric current in a contrary direction to that of the current which we shall call the exciting current. This property of nerves, which, as we shall see, is independent of their vital faculties, is nevertheless connected with their structure, and ceases when the integrity of that structure is impaired. All porous bodies, whether organic or inorganic, when saturated with a conducting liquid, are capable of acquiring a secondary electromotor power, so as to become a sort of secondary pile of Ritter; but I do not enter into an examination of these phenomena, which have been studied in their generality by other physicists, my principal aim being to determine exactly the conditions of the secondary electromotor power of nerves, in order to make a due application of these conditions to the explanation of the electro-physiological phenomena which are awakened at the opening of the voltaic circuit.

On the electrical phenomena which accompany muscular contraction

Dr. Radcliffe has recently communicated to the Royal Society some observations on the nature of the electrical phenomena accom­panying muscular contraction. It is known that M. du Bois-Rey-mond admits that the muscular current diminishes during contrac­tion, and that he attributes the phenomena indicated by the galva­nometer to the momentary predominance of currents due to the polarization of the electrodes of platinum over the muscular current. In my last memoir on Electro-physiology, which was communicated to the Royal Society and appeared in the Philosophical Transactions for 1856, I proved that these phenomena take place independently of the existence of secondary currents of the electrodes, and I hence concluded, at least as regards the muscles of frogs, that during con­traction there is a current, or rather an instantaneous electrical discharge, which takes a contrary direction to that of the relaxed gastrocnemius , and in general to that of the current which is found on applying the extremities of the galvanometer to the extremities of the limbs of a frog. In order to avoid the influence of secondary polarity, M. du Bois-Reymond, and after him several other German physiologists, have thought it expedient to contract and tetanize the gastrocnemius before closing the circuit of the galvanometer; the deviation thus obtained is feebler than that which is due to the current of a muscle in repose, but never in a contrary direction to that due to this current.

I. The following letter was read, from Professor Hansteen of Christiania, For. Mem. R. S

To the Royal Society of London . As a Corresponding Member of the Royal Society, I have the honour herewith to transmit a Research “On the Secular Changes of the Magnetical System of the Earth, and more specially on the Secular Variation of the Magnetical Inclination in the Northern Temperate Zone,” separately printed from the ‘Memoirs of the Roy. Soc. of Sciences of Copenhagen.’ By calculating newer and more ancient observations of the magnetical declination, I have ascertained the movement of the four magnetical polar regions, which I had already found in my work 'Untersuchungen iiber den Magnetismus der Erde’ (Christiania, 1819, with Atlas); whereof the two northern ones have a motion from west to east, the two southern ones in the contrary direction; and have attempted thereby in general to declare the cause of the known variations, as well of the system of declination as of that of inclination and of intensity.

4. On a Mechanical Theory of Thermo-Electric Currents.

It was discovered by Peltier that heat is absorbed at a surface of contact of bismuth and antimony in a compound metallic conductor, when electricity traverses it from the bismuth to the antimony, and that heat is generated when electricity traverses it in the contrary direction. This fact, taken in connection with Joule's law of the electrical generation of heat in a homogeneous metallic conductor, suggests the following assumption, which is the foundation of the theory at present laid before the Royal Society.

Experiments on the influence of magnetism on polarized light

The object of this notice is to communicate some recent experi­ments on diamagnetism, and particularly on the influence of mag­netism on polarized light. The following extracts are in the words of the author :— The apparatus I employed in these experiments was an electro­magnetic apparatus invented by M.Rumkorf, and described by M.Biot at a meeting of the Academy of Sciences of Paris, and consisting of a powerful electro-magnet, of which the soft iron cylinder is traversed by a hole in the direction of the length of the axis, through which hole the ray of polarized light is made to pass; and the voltaic cur­rent which I employed on this occasion was that of seven pair of Grove’s construction. I made my first experiment with a piece of heavy glass, which I received from Faraday himself. In order to assure myself of the exact amount of rotation induced by magnetic action, I caused the ray of light, before it reached the heavy glass , to pass through the system invented by M. Soleil, consisting of two equal plates of perpendicular quartz, placed side by side; the one turning to the right, the other to the left. I ascertained, first of all, the rotation produced by making the current pass sometimes in one direction, and sometimes in the other ; the two rotations, one to the right, the other to the left, thus produced, were exactly the same. Then I compressed slightly the middle part of the piece of heavy glass, in the same manner as one compresses pieces of glass. I was then obliged to turn the eyepiece in a certain direction in order to restore the image to its first condition; in my experiments I always had to turn it, after compression, towards the right. I next made the current pass, first in one direction, then in the other. The ge­neral facts which I have observed constantly and without exception are the following :— The rotation produced by the magnet on the com­pressed piece of heavy glass is not the same to the right as it is to the left: the rotation produced by the magnet is considerably greater in the direction of the rotation produced by compression than it is in the contrary direction: the rotation produced by the magnet on the com­pressed heavy glass, and in the direction of the rotation produced by the compression, is greater than that produced by the same magnet on glass which has not been compressed, and the rotation in the contrary direc­tion is less. The following are the numerical results . “In one experiment I obtained on a piece of heavy glass not com­pressed, 3° of rotation to the right or to the left, according to the direction of the current: on slightly compressing the glass, I had to turn to the right the eyepiece to 4°, 5°, and even to 8° in order to restore the image to its first condition. In closing the circuit, the rotation produced in the same direction as that due to compression wras 3½° or 4°, while the rotation produced in the contrary direction was from 2° to 1½°. On ceasing to compress the glass, I obtained the same phenomena as I had observed before the compression.

Researches on the function of the intercostal muscles and on the respiratory movements, with some remarks on muscular power, in man

The object of this paper is to demonstrate by models and dissections the action of the intercostal muscles. After premising an account of the views of several eminent physiologists, and in particular those promulgated by Haller, the author shows that they resolve themselves into the general opinion that the scalene or other muscles of the neck fix the first rib, in order to enable the two sets of intercostal muscles to act either separately or conjointly, as inspiratory or expiratory muscles. He then proceeds to state the proofs that the intercostal muscles possess an action which is independent of any other muscle, and also independent of each other, so that any of the twelve ribs may be elevated or depressed by them either separately or conjointly. He demonstrates the nature of this action by means of models, producing oblique tensions between levers representing the ribs, and allowing of rotation on their centres of motion; and he shows that such tension in the direction of the external intercostal muscles, elevates both the levers until the tension ceases, or the position of the bars by proximity obstruct each other. If the tension be exerted in a contrary direction, as in the internal intercostal muscles, the bars are both depressed. This movement was demonstrated by a model. It was farther shown that two tensions decussating can, according to the position of the fulcra, be made to act as associates or antagonists to each other. Such motions are to be considered with reference to the fulcra, bars with one fulcrum common to each having no such action; and the author accordingly draws the following conclusions:— 1st. All the external intercostal muscles are true inspiratory muscles, elevators of the ribs, and with this act they dilate the intercostal spaces, thus increasing the cavity of the chest.

Electro-physiological researches.—Fourth memoir

In the prosecution of his inquiries on the physiological action of electric currents, the author found it necessary to employ an apparatus, which was expressly made for him by M. Bréguet, adapted to the delicate appreciation of the intensity of the force of the mus­cular contractions excited by those currents; of which apparatus he gives a minute description, illustrated by a drawing. He was thus enabled to institute an exact comparison between the contrac­tions caused by the direct, and those by the reverse currents, both at the commencement and at the termination of their action. The following are the general conclusions he deduces from the experi­ments thus conducted. 1. The passage of the electric current through a mixed nerve pro­duces a variation in the excitability of the nerve, differing essen­tially in degree, according to the direction of the current through the nerve. This excitability is weakened and ultimately destroyed; and this takes place more or less rapidly according as the direct current , that is, a current circulating through the nerve from the centre to the periphery, is more or less intense. On the other hand, by the passage of the same current in the contrary direction, that is, from the periphery to the centre, or the inverse current , the ex­citability is preserved and increased.

Experimental re­searches in electricity. Twenty-third series. § 29. On the polar or other condition of diamagnetic bodies:

The author, whilst developing, on a former occasion, the pheno­mena of diamagnetic action, said that all the results might be ac­counted for by assuming that bismuth, phosphorus, &amp;c., when in the magnetic field, became polar as iron is polar, but with the poles in the contrary direction. This view has since then been adopted by Weber and others, and supported by certain experimental results. In the present paper these results and that view are brought under very close examination. An apparatus was constructed by which a cylinder of any given metal could be moved to and fro through about two inches in the direction of its axis. In doing this it approached close up to, and then retreated from the pole of an electro-magnet, and also moved within a helix of covered wire which was fixed in relation to the magnet. Norv the action of such a piece of metal upon the helix is very different in theory, and also in reality, according as it is dependent upon a polarity, magnetic or diamag­netic, acquired by the metal, or upon induced currents existing in the mass; and the question was to ascertain by experiment whether the latter were the cause of the results obtained by Weber and others. The various diamagnetic metals gave the results looked for at the indicating galvanometer; but then these were almost insensible with bismuth, and were greatest with gold, silver, copper, and the better conductors, being indeed in proportion to the conducting power. Such results were in favour of induced currents rather than of polarity. Division was next resorted to as a distinguishing test of the polar or current action; thus a cylinder made up of lengths of wires acted as well as a solid cylinder, if the metal were one acquiring a polar state as iron; but such a division interfered with the existence of induced currents in the mass, and it was found that such wire cylinders of copper, &amp;c. lost all power. On the other hand, division of the cylinder into innumerable discs interfered greatly with polarity, but not at all with the induced currents, nor with the action of the diamagnetic metals. ' The places of maximum and minimum action of a cylinder of metal are very different according as that metal acts by a polar condition, or by currents induced in the mass: it is shown by experiments with the diamagnetic metals that their places of maximum and minimum action accord with the effects of induced currents. Time has great effect over results produced by currents induced in the mass, and none over those due to polarity. By this test the effects of the diamagnetic metals are found due to induced currents. The phenomena produced by the use of the present apparatus are then shown to be in close and direct relation to the phenomena of revulsion formerly described by the author: the parallel is closely carried out and extended, and both sets of effects referred to one and the same cause.

VI. On the diurnal variation of the magnetic declination at St. Helena

It has long been known that in Europe the north end of a magnet suspended horizontally (meaning by the north end the end which is directed towards the north), moves to the East from the night until between 7 and 8 o’clock in the morning, when an opposite movement commences, and the north end of the magnet moves to the West . Recent observations have shown that a similar movement takes place at the same hours of local time in North America, and that it is general in the middle latitudes of the northern hemisphere. It has also been known for some years past, and has been confirmed by recent observations, that in the middle latitudes of the southern hemisphere, the north end of the magnet moves in a contrary direction to that which has been described as taking place in the northern hemisphere, viz. that it moves to the west until 8 o’clock in the morning, or thereabouts, and then returns towards the east.

Experimental researches in electricity—Second series

The success of the author in exhibiting the evolution of electricity by induction from ordinary magnets, led him to conclude that similar effects might be obtained from the magnetism of the earth, and even to an extent that might render it available in the construction of new electrical machines. These expectations have been fully realized; and the researches which establish the influence of terrestrial induction in giving rise to electrical currents, form the subject of this second paper. Whenever a hollow helix, the terminal wires of which were connected with those of a galvanometer, and which inclosed a cylinder of soft iron, was held with its axis in the line of the magnetic dip, and suddenly inverted, the evolution of electric currents was immediately rendered sensible by the deflection of the needle of the galvanometer; a deflection in the contrary direction being produced the moment the helix was again inverted, so as to recover its first position. The same effect resulted from the simple introduction of the iron cylinder into, or its removal out of, the helix; evidently in consequence of the magnetism acquired by position with relation to the magnetic poles of the earth. When a cylindric magnet was substituted for the soft iron, the same phænomena, obviously ascribable to terrestrial induction, were in either case observed. Similar but more feeble indications of the same effect were obtained by inverting the helix alone, without its association with any ferruginous body whatever.

Experimental researches in electricity

This paper is divided into four parts: the first being on the Induction of Electric Currents; the second, on the Evolution of Electricity from Magnetism; the third, on a new Electrical Condition of Matter; and the fourth, on Arago’s Magnetic Phænomena. The author defines electrical induction to be the power which electrical currents possess of inducing any particular state upon matter in their immediate neighbourhood. A great length of copper wire, 1-20th of an inch in diameter, was wound round a cylinder of wood so as to compose two helices, the coils of which were intermixed, but prevented from touching each other by interposed threads of twine and calico. One helix was connected with a voltaic battery, and the other with a galvanometer. No effect was perceived on the latter, with a battery of 10 plates; a slight effect only with one of 100 plates; and a distinct deflection of the needle of the galvanometer occurred when the contact was made with a battery of 120 plates. While the contact was preserved, the needle returned to its natural position, and was unaffected by the electric current passing through the wire connected with the battery; but on breaking the connexion, the needle of the galvanometer was again deflected, but in a direction contrary to that of its former deflection. Hence it is inferred that the electric current sent by the battery through one wire, induced a similar current through the other wire, but only at the moment the contact was made; and a current in the contrary direction when the passage of the electricity was suddenly interrupted. These transitory currents, resembling waves, were found to be capable of magnetizing needles placed within the helix. Collateral currents, either in the same or in opposite directions, exert no permanent inductive power on each other.

On the mutual action of the particles of magnetic bodies, and on the law of variation of the magnetic forces generated at different distances during rotation

The results obtained by the author, described in a former communication, when a copper disc was made to revolve under a magnetized needle, appearing to him not likely to lead to an accurate knowledge of the law of magnetic attraction, developed during rotation, from the effect of lateral attraction; he was induced to resume the inquiry, substituting a ring for a disc, expecting that, as no lateral forces would here be called into action, the results would be more uniform, and in this expectation he was not disappointed. One of the first phenomena encountered by him in this research, was a very great diminution of magnetic force, when a ring of the same weight was substituted for a disc; and pursuing this point of inquiry, he found that in all cases of solution of continuity, not only by cuts in the direction of radii from the centre, but in concentric annuli or otherwise, there is always a great loss of force, the magnetism of the whole being always much greater than the sum of that of the parts. He describes in detail these experiments, and the apparatus used for them. His method of estimating the intensity of the force developed, was by suspending the body, set in, rotation by a revolving magnet, by a wire, and preserving a constant velocity of rotation in the magnet, to note the time when the velocity acquired by the disc, was just destroyed by the torsion of the wire, and the disc just began to revolve in a contrary direction. Applying analysis to the dynamical problem arising, he thence deduces the intensity of the force urging the suspended body. Applying the resulting formula to the experiments, he finds, in almost ail cases, a small diminution in the intensity of the force as the arc of rotation increases, which he attributes to a very minute degree of magnetism accumulated in the disc, and retained by it till the revolving magnet comes round again. In reasoning on the experiments detailed, Mr. Christie concludes that the greatest developement of magnetism in a disc, subjected to the action of revolving magnets, takes place when the axes of the magnets are vertically under points bisecting the radii, and that the magnetism decreases very rapidly as they approach the edge; thus indicating that for a full development of magnetism, a continuity of substance, in all directions from the point acted on, is principally requisite. This result is corroborated in a striking manner by the effect produced by concentric circular cuts in the disc, leaving the interior attached to the exterior in several places. On successively destroying these points of connexion, a very great diminution of force is perceived.

Remarks on the employment of oblique riders, and on other alterations in the construction of ships. Being the substance of a report pre­sented to the board of admiralty; with additional demonstrations and illustrations

Dr. Young observes, that the question respecting the best dispo­sition of the timbers of a ship is by no means so easily discussed as may be supposed by those who have considered the subject but su­perficially; and deprecates, on the one hand, the forming a hasty determination from a few plausible experiments, as only tending to expose those who are influenced by it to very dangerous errors; and, on the other, the total rejection of the conclusions formed from such experiments without a minute examination of the objections brought against them. He enters into a detailed enumeration of all the force that can act on the fabric of a ship, and into an exact calculation o the probable magnitude of each in such circumstances as are likely to occur; and afterwards considers how far the resistances to be op­posed to those forces are sufficient to withstand their action. The strains which occasion the effect of arching are, he observes, of two kinds; the one derived from the distribution of the weight of the ship, with its contents being not duly proportioned to the pressure of the water; the other, which has not hitherto been noticed, from the simple and unavoidable application of the longitudinal pressure of the water to the lower parts of the ship only, amounting to more than one third as much as the former, in the case of a seventy-four gun ship of the usual dimensions, being equivalent to the effect of a weight of about 1000 tons, acting on a lever one foot in length, while the strain arising from the unequal distribution of the weight, and the displacement, amounts, where it is greatest, to 2600, although it is somewhat less than this exactly in the middle of the vessel. The next force investigated by the author is that of the waves, which he considers as including the consequences of the effect of the wind; and this he finds capable of becoming much greater than the former, amounting, in particular cases of the effect of a series of waves, to a strain of about 10,000 tons, and their difference more than 6000 when the waves are in a contrary direction. Hence it is inferred, that although these occasional strains exceed in magnitude the per­ manent causes of arching, they do not by any means make it super­ fluous to give the greatest strength to the fabric in the direction which is best calculated for the prevention of that effect. It is also remarked, that when fastenings have once given way to an oc­casional force of this land, the ship must naturally assume the form which is determined by the operation of more permanent causes; and this circumstance may lead the inattentive observer to false con­clusions respecting the manner in which the injury has been sustain­ed. The tendency to breaking transversely arises from causes pre­cisely similar to those which have been mentioned as operating longitudinally; but their precise magnitude does not appear to be easily calculable. The force tending to produce a lateral curvature has com­monly been in some measure neglected, for want of a permanent strain in a similar direction, capable of exhibiting its effects; but Dr. Young estimates its magnitude, in certain cases of waves striking a ship obliquely, to be nearly or fully equal to that of the vertical strain, as already computed. The manner in which a ship gives way when she strikes the ground is next described; and the effects of partial moisture in promoting decay are mentioned as the last of the evils which it is the object of the builder to obviate, as far as it is in his power. Dr. Young proceeds to consider the arrangements that are best adapted to obviate the various strains which are likely to occur in the fabric of a ship, and observes, that the principal, if not the only, ad­vantage of oblique timbers is in the additional stiffness which they afford; since the ultimate strength, or the resistance at the point of breaking, is little, if at all, affected by them in the cases which have been proposed for experimental examples, though, in some other cases, the strength as well as the stiffness may be surprisingly in­creased by the obliquity of the substances employed.