Feeble Currents Research Articles

Revolving and Evolving-Early dc Machines [Historical

In an age largely characterized by information and communication technology, which uses more and more feeble currents, electrical power is experiencing a period of excellent health and heading toward a bright future. This success is largely due to electric motors, which are available in different types and powered by dc as well as ac sources operating at either utility or variable frequencies. The versatility and ubiquity of electric motors are so wide that they can be found almost everywhere: in many household appliances, technician power tools, building fans, factory machine tools, blowers and pumps of industrial fluid systems, cableways, railway and streetcar locomotives, computer disk drives, drivers and printers, and cell phone vibration alerts.

Leopoldo Nobili: His Galvanometer and His Connections to the Faraday-Neuman-Lenz Law of Induction

The discovery of the phenomenon of magnetic induction, or the Faraday-Neumann-Lenz law of induction, was something much expected, after Hans Christian Ørsted [Rudk⊘bing, Benmark, August 14, 1777 - Copenaghen, Denmark, March 9, 1851] discovered that electric currents had an effect on a magnetic needle. Many researchers, among whom the most notable was Michael Faraday [Southwark, London, UK, September 22, 1791 — Hampton Court, Middlesex, UK, August 25, 1867], actively sought such a phenomenon, yet the instrumentation then available was exceedingly crude [1]. For an electric phenomenon to be apparent, a spark should be o bserved for voltage, or a current strong enough for visible effects. Some more-sensitive device able to detect feeble currents was necessary. Indeed, Orsted's discovery made possible the development of such an instrument: the galvanometer. In that same 1820, Johann Schweigger [Erlangen, Germany, April 8, 1779 - Halle, Germany, September 6, 1857] build a first galvanometer by winding a coil of wire around a magnetic needle free to rotate. This was later enhanced by multiplying the effect of the current by using several coils of wire.

Direct Electrical Measurements on Single-Molecule Genomic DNA Using Single-Walled Carbon Nanotubes

A unique nanoelectronic platform, based on single-walled carbon nanotubes (SWNTs), has been fabricated for measuring electrical transport in single-molecule DNA. We have tested 80 base pairs of single- and double-stranded DNA (ssDNA and dsDNA, respectively) of complex base sequences. About a 25-40 pA current (at 1 V) was measured for the dsDNA molecule covalently attached to the SWNT electrode at its termini. In the absence of base pair stacking, a ssDNA carries a feeble current of approximately 1 pA or less. Gate-voltage-dependent I-V characteristics revealed that the bridging dsDNA molecule acts as a p-type channel between SWNT source and drain electrodes.

Scleractinian assemblages under sediment input: their characteristics and relation to the nutrient input concept

In the geological record, scleractinian-dominated “turbid-water” bioconstructions that accumulated under substantial terrigenous input, along with shallow neritic marls rich in well-preserved corals are common. These occurrences indicate that beyond some threshold, the ecologic and taphonomic effects of sedimentation prevail over the effects of nutrification. Field data and experiments on recent corals show that some taxa cope well with terrigenous turbidity and sedimentation, and acclimate to increased heterotrophy. Colonial corals resilient to sediment input commonly are massive to platy forms of high skeletal plasticity and with large polypars, to effectively reject sediment, or are branched species providing a very small sedimentation area cleaned by feeble currents, or small-polyped massive taxa that tolerate intermittent veneering by sediment. These corals may comprise “siltation assemblages” of recent turbid-water reefs and level-bottoms, in siliciclastic environments. Conversely, excess input of even low amounts of dissolved inorganic nutrients into clear waters adversely affects many coral species. Fossil turbid-water bioconstructions (TWB) were situated in inner shelf to shore zone settings or near storm wave base on shelves or ramps, did not stack into reef complexes, mostly show a cluster to segment fabric, are scarce in or devoid of frame pores with marine cement, and lacked a high carbonate slope. Relative to fossil “clear-water” buildups preserved in pure limestone successions, fossil TWB contain (moderately) diverse coral assemblages, with an increased proportion of sediment-resistant forms. Aside from coral behaviour that is elusive in fossils, the sediment resistance of corals was mainly determined by colony shape and polypar size, but small-polyped, sediment-tolerant corals became common since the Early Cretaceous. Late Jurassic to Cretaceous turbid-water coral assemblages are dominated by plocoid or thamnasterioid forms; corresponding Cainozoic assemblages consist mainly of cerioid and plocoid taxa. In fossil TWB, bioerosion and encrustation are similar or higher than in contemporaneous clear-water buildups. Under higher sediment input, accumulation of discrete TWB was quenched, and level-bottoms of both corals and soft-substrate biota formed. In the resulting “coral marls”, depending on turbidity, sedimentation and substrate stability, the coral fauna consists largely of both solitary corals and (mainly) sediment-resistant pseudocolonial/colonial forms, or is dominated by solitary corals. Many corals show growth “anomalies” resulting from partial mortality due to episodic, rapid sedimentation and unstable substrate. In coral marl environments, because of terrigenous input, nutrient levels probably were elevated, yet macroboring and encrustation are very scarce. Beyond some threshold of terrigenous sediment input and accumulation, the ecologic and taphonomic effects of sedimentation and unstable substrate prevail over the effects of nutrient enrichment. During the Meso-Cainozoic evolution of scleractinians, increasing photoautotrophy and progressive invasion of oligotrophic environments is in contrast to a Late Cretaceous to Cainozoic increase in the relative number of reefs in marginal-marine/siliciclastic settings. This trend may be explained by second-order sea-level fall and shrinking of epicontinental carbonate seas and isolated platforms, driving corals to more narrow, attached shelves, and by a wider total trophic range in which distinct coral assemblages can thrive, as a result of coral evolution and diversification.

Catalytic activity of birch charcoal in the dehydrogenation of cyclohexane

1. An investigation was made of the catalytic activity of birch charcoal in the dehydrogenation of cyclohexane to benzene at 600° in the course of the prolonged working of the catalyst. It was found that after 33 hr of work the dehydrogenating activity of the charcoal fell to about 50% of its initial activity. As by-products we then obtained small amounts of methylcyclopentane, cyclohexene, and C6 alkanes, the contents of which rose as the catalyst became inactivated for the dehydrogenation of cyclohexane. 2. Regeneration of the activated birch charcoal with steam or by oxidation with a feeble current of air at the temperature of the experiment led to the recovery of its initial activity.

The wave antenna a new type of highly directive antenna

The wave antenna a new type of highly directive antenna

The Wave Antenna A New Type of Highly Directive Antenna

The Wave Antenna A New Type of Highly Directive Antenna

The Thermionic Valve in Wireless Telegraphy and Telephony1

THE thermionic valve is an invention which has vastly increased the powers and range of wireless telegraphy. Like many other inventions, the telephone, for instance, it is simple in its essential construction. It consists of a little electric lamp comprising a glass bulb, very highly exhausted of its air, containing a filament of carbon, or better tungsten, which can be rendered incandescent by an electric current. Within the bulb and around the filament are fixed certain metal plates or cylinders, and, it may be, spirals of wire or metal networks called the grid. To explain its origin in its simplest form I shall have to take you back in thought to the days when the physical effects taking place in incandescent electric lamps were first beginning to be considered carefully. In 1883 Mr. Edison for some purpose placed in the glass bulb of one of his carbon filament lamps a metal plate which was carried on a platinum wire sealed through the glass. When the filament was rendered incandescent by a current from a battery, he found that if the plate was connected by a wire, external to the lamp, with the positive terminal of the filament, a small electric current flowed through it, but if connected to the negative terminal no current, or at most a very feeble current, flowed. This new and interesting effect became known as the “Edison effect” in glow lamps, but Mr. Edison gave no explanation of it, and made no practical application of it.

Societies and Academies

LONDON. Royal Society, January 28.—Sir William Crooks, president, in the chair.—W. W. C. Topley: The influence of salt-concentration on haemolysis. The method employed in this investigation has consisted in varying the percentage of sodium chloride present in a mixture of sheep's red cells, hæmolytic anti-body and complement. The hæmolytic anti-body was obtained from an immunised rabbit, and fresh guinea-pig serum, previously absorbed with sheep's red cells at 0° C, furnished the complement. Where hypotonic percentages of sodium chloride have been employed, the solutions have been made in 7.8 per cent. saccharose solution. The results have confirmed the observations of other workers that, when the percentage of salt is increased beyond the normal limit, hæmolysis is inhibited, owing to the failure of union between the complement and the red-cell anti-body complex, and that, if the amount of anti-body present in the mixture be increased, the effect of the increased salt concentration may to a certain extent be overcome. It has further been shown that, if the salt concentration be decreased below the normal limits, less and less anti-body becomes necessary in order to bring about the union of red cells and complement, and that, in the almost entire absence of electrolytes, guinea-pigs' complement can hæmolyse sheep's red cells without the intervention of hæmolvtic anti-body.—G. Smith: The life-cycle of Cladocera, with remarks on the physiology of growth and reproduction in Crustacea. As the result of breeding experiments, it is shown that the effects of isolation, crowding, and temperature are the same for Daphnia pulex as previously reported for Moina rectirostris, viz., isolation combined with high temperature completely inhibits the production of sexual individuals, reproduction being entirely parthenogenetic. Crowding, combined with low temperature, results sooner or later in the production of males and ephippial females.—T. Goodey: Investigations on protozoa in relation to the factor limiting bacterial activity in soil. Two different lots of soil were taken and inoculated with cultures of protozoa originally obtained from soil, in order to determine whether the added protozoa would cause a decrease in the numbers of bacteria in the soil. One soil was free from protozoa to begin with, having been bottled since 1846, whilst the other was freed from protozoa by partial sterilisation. Separate lots of each soil were inoculated with cultures of ciliates, amoebae, and flagellates, and suitable control sampleswere set up. Periodical bacterial counts were made inorder to ascertain if the protozoa were exerting a limiting action on the soil bacteria, and these counts were continued over a period of about eighteen months. The general conclusion drawn from the investigations is that ciliates, amoebae, and flagellates do not act as the factor limiting bacterial activity in soil.—S. Hatta: The mesodermic origin and fate of the so-called mesectoderm in petromyzon. The name mesectoderm has given to a loose aggregation of mesenchymatous tissue, in some places assuming the character of an epithelium intervening between the myotomes and the ectoderm in the head and branchial region of the embryo of petromyzon. As the name implies, it has been confidently asserted that this tissue is derived from the ectoderm. In this paper, however, it is shown that this tissue originates from the ventral edge of the myotome and corresponds to the ventral extension of the myotome in the trunk region which grows downwards towards the mid-ventral line outside the splanchnocœle and gives rise to the ventral muscles of the trunk.—Prof. J. C. Bose: The influence of homodromous and heterodromous electric currents on transmission of excitation in plant and animal. The action of an electric current in inducing variation of conductivity may be enunciated under the following laws, which are equally applicable to the conducting tissue of the plant and the nerve of the animal:—(1) The passage of a current induces a variation of conductivity, the effect depending on the direction and intensity of current. (2) Under feeble intensity, heterodromous current enhances and homodromous current depresses the conduction of excitation. (3) The after-effect of a feeble current is a transient conductivity-variation, the sign of which is opposite to that induced during the continuation of current. (4) The normal conductivity-variation undergoes a reversal under a strength of current above the critical value. The heterodromous current then induces a depression while the homodromous current induces an enhancement of conductivity.

Reports on the Marine Biology of the Sudanese Red Sea.-XVIII. A Physical Description of Khor Dongonab, Red Sea.

SUMMARY 1 There have been three successive lines of barrier reef along the Red Sea Coast, which, by continual uplift, have become: 1 A range of sandstone hills rising from the alluvial maritime plain; 2 A fringe of limestone along the present coast-line; 3 The present barrier system. 2 These three ridges were formed by folding and faulting of sedimentary-rocks which overlay the bases of the Archean hills at the time of the great movement which opened the Red Sea section of the Great Rift Valley. 3 The northern ends of several sections of the present barrier reefs are elevated above sea-level, and examination of these, especially the one forming Rawaya Peninsula, and of the hills forming the maritime plain, enables us to reach the above conclusions. At the same time Rawaya gives evidence of a seaward movement as well as uplift, Khor Dongonab and some at least of the channels within the Barrier Reefs being recent fault-depressions, not merely the original anticlinal fold formed by the opening of the Rift Valley. The harbours and other fissures in the coast are due to the same secondary faulting. 4 The maritime plain has had two maxima of seaward extension, the first being before, the second after the growth of coral on the second and third barriers. Owing to elevation nothing has been added to its seaward slopes since the formation of the features of the coast by secondary faulting. 5 The filling in of valleys and the completion of the connection of the second barrier with the maritime plain has been largely due to blown sand. The process is continuing, an extensive plain near Dongonab showing perfect uniformity in its formation. The effect of climate and vegetation on the formation of the plain is described (Plate 34). 6 Of the possible mode of formation of the widely distributed gypsum deposits the theory favoured is by the evaporation of a shallow sea which is presumed to have existed before the deep Rift Valley was made. The recent and still continuing deposition of gypsum beneath the Rawaya salt field is an interesting actual example of this method. 7 The restriction of coral growth within Khor Dongonab, a very exceptional it' not unique state of things in the Red Sea, is shown to be the result of abrasion by silt-carrying currents. Considerable effects follow from comparatively feeble currents which curry very little sand, but that this is sufficient to prevent the fixation of coral larvae is borne out by the comparison of newly fixed spat of those mollusca which do flourish on these current-swept banks with those of the Aviculidae, e.g., which flourish on the coral areas. 8 That on its west shore Khor Dongonab is extending itself at the expense of the land in spite of the presence, in some abundance, of coral and Lithothamnia. The presence of these must not be assumed to imply the addition of material to a reef unless their growth can more than counterbalance the forces of degradation.

I. Note on the development of feeble currents by purely physical action, and on the oxidation under voltaic influences of metals not ordinarily regarded as spontaneously oxidisable

In the course of a series of further experiments on cells set up with “aeration plates” (plates simultaneously in contact with the air and the electrolytic fluid used in the cells—‘Roy. Soc. Proc.,’ vol. 42, p. 212), we have made a large number of determinations of the E. M. Fs. developed with incorrodible aeration plates of various kinds ( e. g ., platinum foil, spongy platinum, thin sheet gold, &c.) when opposed to the same oxidisable metal, such as copper or zinc, in contact with the same electrolytic fluid, e. g ., dilute sulphuric acid or caustic soda solution.

IV. On the dark plane which is formed over a heated wire in dusty air

In the course of his examination of atmospheric dust as rendered evident by a convergent beam from the electric arc, Professor Tyndall noticed the formation of streams of dust-free air rising from the summits of moderately heated solid bodies. “To study this effect a platinum wire was stretched across the beam, the two ends of the wire being connected with the two poles of a galvanic battery. To regulate the strength of the current a rheostat was placed in the circuit. Beginning with a feeble current, the temperature of the wire was gradually augmented; but before it reached the heat of ignition, a flat stream of air rose from it, which, when looked at edgeways, appeared darker and sharper than one of the blackest lines of Fraun­hofer in the solar spectrum. Right and left of this dark vertical band the floating matter rose upwards, bounding definitely the non-luminous stream of air.”.... “When the wire is white hot, it sends up a band of intense darkness. This, I say, is due to the destruction of the floating matter. But even when its temperature does not exceed that of boiling water, the wire produces a dark ascending current. This, I say, is due to the distribution of the floating matter. Imagine the wire clasped by the mote-filled air. My idea is that it heats the air and lightens it, without in the same degree lightening the floating matter The tendency, therefore, is to start a current of clean air through the mote-filled air. Figure the motion of the air all round the wire. Looking at its trans­verse section, we should see the air at the bottom of the wire bending found it right and left in two branch currents, ascending its sides, and turning to fill the partial vacuum created above the wire. Now as .each new supply of air, filled with its motes comes in contact with the hot wire, the clean air, as just stated, is first started through the inert motes. They are dragged after it, but there is a fringe of cleansed air in advance of the motes. The two purified fringes of the two branch currents unite above the wire, and, keeping the motes a once belonged to them right and left, they form by their union the dark band observed in the experiment. This process is incessant. Always the moment the mote-filled air touches the wire, the distribu­tion is effected, a permanent dark band being thus produced. Could the air and the particles under the wire pass through its mass, we should have a vertical current of particles, but no dark band. or here, though the motes would be left behind at starting, they would hotly follow the ascending current, and thus abolish the darkness.

On the Dark Plane Which is Formed Over a Heated Wire in Dusty Air 1

IN the course of his examination of atmospheric dust as rendered evident by a convergent beam from the electric arc, Prof. Tyndall noticed the formation of streams of dust-free air rising from the summits of moderately heated solid bodies (Proc. Roy. Inst., vol. vi. p. 3, 1870). “To study this eftect a platinum wire was stretched across the beam, the two ends of the wire being connected with the two poles of a galvanic battery. To regulate the strength of the current a rheostat was placed in the circuit. Beginning with a feeble current, the temperature of the wire was gradually augmented; but before it reached the heat of ignition, a flat stream of air rose from it, which, when looked at edgeways, appeared darker and sharper than one of the blackest lines of Fraunhofer in the solar spectrum. Right and left of this dark vertical band the floating matter rose upwards, bounding definitely the non-luminous stream of air.” . . .

The Telephone, an Instrument of Precision

THE applications to which the telephone may in future be put cannot yet be all foreseen. I have to-day had its value shown to me in a remarkable way. 1. I used a thermo-electric intermittent current by drawing a hot end of copper wire along a rasp completing the circuit. A telephone was put into the circuit, in another room, and every time that the wire was drawn along the rasp a hoarse croaking was heard in the telephone. 2. I used a thermopile with a Bunsen burner shining on it from a distance of six feet. The current was rendered intermittent by the file, and the sound was most distinctly heard. A Thomson's reflecting galvanometer was introduced into the circuit which showed that the currents were extremely small. 3. The feeblest attainable currents were now tried. The thermopile was removed, and without any artificial application of heat it was shown by the galvanometer that the natural differences in the temperatures of the different junctions in the circuit were sufficient to generate feeble electric currents only just perceptible with the mirror galvanometer. These were easily detected by aid of the rasp and the telephone. Even when contact was simply made and broken with the hand, a click was heard in the telephone. 4. Lastly, these feeble currents were rendered still more insignificant by passing them through the body of a friend who held one end of the wire in each hand, and still the effects were faintly audible. Here the galvanometer, which was still in circuit, hardly gave any indication.

Observations on the electro-chemical influence of long-continued electric currents of low tension

The author, after observing that the brilliant discoveries in electrochemistry obtained by Sir Humphry Davy were effected by the employment of voltaic currents of high in tensity, elicited by means of large batteries, adverts to the labours of M.Becquerel, to whom we are indebted for the knowledge of the chemical agency of feeble currents in reducing several refractory oxides to the metallic state : and also to those of Dr. E. Davy, Bucholtz, and Professor Faraday in effecting decompositions of other substances by similar means. In prosecuting this branch of inquiry, the author employed an apparatus analogous to that of Professor Daniell, for obtaining an equal and continuous current of low intensity from a single pair of plates : the metallic solution, in which a copper-plate was immersed, being contained in a glass tube, closed at the bottom by a diaphragm of plaster of Paris, and itself plunged in a weak solution of brine contained in a larger vessel, in which a plate of zinc was immersed j and a communication being established between the two metallic plates by connecting wires. By the feeble, but continuous current thus elicited, sulphate of copper is found to be slowly decomposed, affording beautiful crystals of metallic copper. Iron, tin, zinc, bismuth, antimony, lead, and silver may, in like manner, be reduced, by a similar and slightly modified process; in general appearing with metallic lustre, and in a crystalline form, and presenting a remarkable contrast in their appearance to the irregular, soft, and spongy masses obtained from the same solutions by means of large batteries. The crystals of copper rival in hardness and malleability the finest specimens of native copper, which they much resemble in appearance. The crystallization of bismuth, lead, and silver, by this process, is very beautiful; that of bismuth being lamellar, of a lustre approaching to that of iron, but with the reddish tint peculiar to the former' metal. Silver may thus be procured of the whiteness of snow, and usually in the form of needles. Some metals, such as nickel, which, when acted on by currents from large batteries, are deposited from their solutions as oxides only, are obtained, by means of the apparatus used by the author, in a brilliant metallic form. He farther found that he could in this way reduce even the more refractory metallic oxides, such as silica, which resist the action of powerful batteries, and which M. Becquerel could only obtain in alloy with iron. By a slight modification of the apparatus he was enabled to form amalgams both of potassium and of sodium with mercury, by the decomposition of solutions of chlorides of those bases ; and in like manner ammonium was easily reduced, when in contact with mercury by the influence of a feeble voltaic current. In this last experiment it was found that an interruption to the continuance of the current, even for a few seconds, is sufficient to destroy the whole of the product which had been the result of the previous long-continued action; the spongy ammoniacal amalgam being instantly decomposed, and the ammonia formed being dissolved in the surrounding fluid.

Experiment researches on the conducting powers of wires for electricity; on the heat developed in metallic and liquid conductors

In a former communication, published in the Philosophical Transactions for 1833, the author endeavoured to show that the quantity of voltaic electricity conducted, or the force of the current, was a function of a greater number of variables than had been previously supposed. As the theory which he proposed for estimating the conducting powers of substances has been controverted by M. Lenz, he has been induced to reconsider the subject, and finds reason to be satisfied with the correctness of his former views. He farther finds that with feeble magnetic needles the deflecting forces are not proportional to the force of the current, but approach nearer and nearer to that proportion by increasing the magnetic power of the needles; a result which the author thinks is strictly deducible from the universal law of nature, that the attraction mutually exerted by two bodies is measured by the sum of their masses. He shows that the formula of Ohen, expressive of the conducting powers of wires, and of the resistances which they offer to currents of voltaic electricity, is an approximation to the truth only in the case of feeble currents, and that with the same metal, the conducting powers are not as the lengths of the wires. The author next inquires into the relation between the heat developed, which he finds to be, in the same wire, as the square of the intensity of the current; and in wires of the same diameter, and conducting equal quantities of electricity, it is inversely as the conducting power, or directly as the resistance which they oppose to the current. The facts he has adduced in this paper seem to be at variance with the generally received theory of caloric, and to be in perfect accordance with the undulatory theory.

V. Observations on the electro-chemical influence of long-continued electric currents of low tension

1. Scarcely any branch of scientific investigation has yielded more important and interesting results than electro-chemistry, which, as is well known, in the hands of a Davy, demonstrated the existence of the alkaline metals, and formed a memorable and important epoch in the history of chemical science. Sir Humphry Davy availed himself of the energetic influence of voltaic currents in a high state of tension, and elicited by means of large batteries. To M. Becquerel, however, we are almost en­tirely indebted for our knowledge of the chemical agency of feeble currents in reducing certain refractory oxides to the metallic state, although it must not be forgotten that Dr. Edmund Davy applied the power of weak currents of electricity to the detection of the metallic poisons, by reducing them to the reguline state. Bucholz appears, in 1807, to have succeeded in obtaining crystals of metallic copper by the aid of a simple voltaic circle. But it is to our illustrious countryman Dr. Faraday that we owe our acquaintance with the interesting circumstance of the power possessed by a current of very low intensity (elicited by a single pair of platinum and zinc plates) in decom­posing several saline combinations, as the iodide of potassium, sulphate of soda, &c., and isolating their respective constituents. In offering the following observations, I have not sufficient presumption to suppose them to be possessed of any very important or original value; but being, as they are, the results of carefully repeated experiments, and containing an account of what I believe to be some previously unobserved facts, I deem myself justified in submitting them to the notice of the Royal Society.