Mean Solar Day Research Articles

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THE NEW ALGOL-TYPE VARIABLE.—Mr. Chandler has been able (Gould's Astronomical Journal, No. 150) to secure some further observations of this star, which, so far as they go, tend to confirm the hypothesis of a period of about three days. Minima were observed on January 2 and 11, but these were inconclusive as to the period. The star was, however, observed on January 12, between 17h. 15h. and 18h. 5m., to be apparently of its normal maximum brilliancy, whereas the first rough elements formed would have given a minimum at 17h. 50m., had the period been 1.4992d. or 0.7496d. Further observations are much desired. It unfortunately happens, from the star's period being very closely commensurable with the mean solar day, that further observations of minima will be scarcely possible in Northern Europe or Eastern North America for many months.

Questions respecting Mr. Stone's Theory of Changes in the Mean Solar Day

Questions respecting Mr. Stone's Theory of Changes in the Mean Solar Day

On the Necessarry Distinction in Practical Astronomy between the True Mean Solar Day and the Mean Day adopted, from time to time, in the Construction of our Astronomical Tables, and in the Comparison of these Tables with Observations

On the Necessarry Distinction in Practical Astronomy between the True Mean Solar Day and the Mean Day adopted, from time to time, in the Construction of our Astronomical Tables, and in the Comparison of these Tables with Observations

Additional Note to Mr. Stone's Paper on the Change in the adopted Length of the " Tabular Mean Solar Day, " which takes place with every Change in the adopted value of the Sun's Mean Sidereal Motion

Additional Note to Mr. Stone's Paper on the Change in the adopted Length of the " Tabular Mean Solar Day, " which takes place with every Change in the adopted value of the Sun's Mean Sidereal Motion

On the Change in the Adopted Length of the " Tabular Mean Solar Day, " which takes place with every Change in the Adopted Value of the Sun's Mean Sidereal Motion

On the Change in the Adopted Length of the " Tabular Mean Solar Day, " which takes place with every Change in the Adopted Value of the Sun's Mean Sidereal Motion

Our Astronomical Column

THE SATURNIAN SATELLITE, HYPERION. — Prof. Asaph Hall, in Astron. Nach., No. 2,137, publishes an ephemeris of this faint object about the approaching opposition of Saturn, with the view to facilitate observations, especially near the conjunctions. He remarks that although the satellite was discovered (by Bond and Lassell) nearly thirty years since, the difficulty of observing it has been so great that no satisfactory determination of its orbit has been practicable; most of the observations being made near the elongations, the position of the plane of the orbit is not accurately deducible therefrom, though it probably does not coincide with the plane of the ring, but appears to lie between those of Titan and Japetus. With the view to assist observation in the present year Prof. A. Hall has calculated elements from his observations in 1875, which may be stated as follows:—Perisaturnium passage. 1875, August 24.0036 mean time at Washington; distance of perisaturnium from the node 40° 0′, eccentricity 0.125, semi-axis major 214″.22, period of revolution 21.3113 mean solar days. For the reason stated above it is supposed for this approximate orbit that its plane coincides with that of the ring, the node of which on the earth's equator is assumed to be in 126° 9′.1, and its inclination thereto 7° 3′.8. From these data auxiliary quantities and an ephemeris for Washington midnight, August 1-September 15, are added, and it is suggested that with the aid of the former comprising the interval June 1-December 28 a more accurate calculation may be made by Mr. Marth's formulae.

Measurement of Mass and Force

“W. M. W.” seems to regard units of mass and force as things which are to be talked and philosophised about, rather than to be actually used for the measurement of concrete qualities. It is true that the force of gravity on a standard pound at a specified locality is a definite unit of force; but instead of specifying a locality to which reference is by common consent to be made (and without which consent we shall have as many different units as there are localities), he says, “The assumption of a hypothetical force of gravity not dependent on latitude seems to stand on the same footing as the employment of a mean solar day.”

Observations made with the invariable pendulum (No. 4. Jones), at the royal observatory, cape of good hope, for the purpose of determining the compression of the earth

Of the two methods employed for determining the figure of the earth, namely, the direct measurements of arcs of the meridian, or of ascertaining the variations in the length of the seconds pendulum in different places, the author remarks that the former is attended with the collateral benefit of fixing the geographical position of certain stations in the country surveyed; but the latter possesses the advantage of enabling the observer to concentrate, under his own immediate eye, the results of his inquiries. The Observatory at the Cape of Good Hope having been furnished by the Lords Commissioners of the Admiralty with the invariable pendulum of Jones, which had for several years been strictly examined by Capt. Sabine, the author was anxious to begin a series of experiments with it; and as it was not likely that the observatory would be completed for a considerable time, he caused a strong brick pier to be built in an adjoining outhouse for the support of a transit instrument, the same which he had used in forming his catalogue of southern stars. He gives a detailed account of his mode of fitting up the clock, and other parts of the apparatus necessary for the pendulum experiments. He was ably assisted by Capt. Ronald and Lieut. Johnson, who took an active part in all the observations. He remarks, that the near agreement of the three independent series of observations, made by himself and these two gentlemen, and which accompany the paper, is no small argument in favour of their accuracy. The difference in the number of vibrations of the seconds pendulum at the Cape, from that in London, in a mean solar day, he finds to be 67·12, from which it results that the compression of the earth is 1/288.5. The author is of opinion that the invariable pendulum ought to be a standard instrument in every observatory; that it should be swung at all seasons of the year, and occasionally transferred to various fixed observatories in both hemispheres, and returned again to its original station, where it should undergo a renewed and rigid examination before it is sent round on a fresh circuit of these stations.

Experiments to determine the difference the number of vibrations made by an invariable pendulum in the royal observatory at Greenwich, and in the house in London in which Captain Kater’s experiments were made

The experiments of which an account is given in this paper, were made in compliance with a request of the Council of the Royal Society, made in December 1827, that Captain Sabine would ascertain the difference in the number of vibrations of a pendulum at Mr. Browne’s house, and at the Greenwich Observatory. The author gives a description of the instruments used in the observations; the first series of which were made in Mr. Browne’s house, from the 17th to the 20th of March inclusive, and gave as the mean result, 85963·60 vibrations in a mean solar day. A reduction is here introduced, derived from some experiments made on the difference which takes place in the times of vibration in vacuo and in air; the number of vibrations in the former case being, under the same circumstances as in the observations, 9·97 per diem less than in the latter. A corresponding series made at Greenwich in May, gave as the mean 85964·17 vibrations, thus indicating an acceleration of 0·57 vibrations per diem , but the difference of latitude and of height between the two stations would have led us from theory to expect a total retardation of 0·38 vibration in the same time. From a second set of observations at Greenwich, the diurnal acceleration appeared to be 0·52 vibration. Taking the mean of this and the former result, it appears that the total amount of the discordance between theory and experiment is 0·91 vibration per diem . The stations are conveniently situated for verifying the existence of this anomaly, and its magnitude is such as to preclude all uncertainty as to its existence. With regard to its cause, the author is confirmed in the opinions he formerly entertained on this subject. Tables are subjoined, containing accounts of the rate of the clocks used at both stations, and of the particulars of each series of observations.

An account of experiments made with an invariable pendulum at new south wales, by Major-General Sir Thomas Brisbane, K. C. B. F. R. S. Communicated by Captain Henry Kater, F. R. S., in a letter to Sir Humphry Davy, Bart. P. R. S

In this communication, laid before the Royal Society at the request of Sir Thomas Brisbane, Captain Kater gives the results of experiments made by Sir Thomas Brisbane and Mr. Dunlop, at Paramatta, in New South Wales; and by Sir Thomas Brisbane, Captain Kater, and Mr. Rumker, in Portland Place, London, with an invariable pendulum belonging to the Board of Longitude. The number of vibrations made by this pendulum in a mean solar day at London, in latitude 51° 31' 8" 4, at the temperature of 60°, and reduced to a vacuum, was found to be 86090·17: at Paramatta, in latitude 33° 48' 43'' S., by Sir Thomas Brisbane’s experiments 86021·59; and by those of Mr. Dunlop 86022·21.

An account of experiments to determine the acceleration of the pendulum in different latitudes

The clocks and pendulums used in these experiments are the property of the Royal Society, and were prepared by their direction, under the superintendance of Captain Kater, whose description of them is quoted by the author at the commencement of this paper. The experiments were made during two voyages of discovery in search of a North-west Passage, the first in 1818, and the second in 1819 and 1820; and Captain Sabine details in succession the proceedings at each station, where an opportunity was afforded of landing and setting up the clocks; and concludes by recapitulating the number of vibrations made by each pendulum in the different latitudes in which it was tried, and by stating the deductions regarding the figure of the earth which follow from the acceleration thus determined. In the first voyage, the number of vibrations was ascertained at two stations only; namely, at Gardie House on the Island of Brassa, and on Waygat, or Hare Island, on the West coast of Greenland; the latitude of the first being 60° 9' 42" N., and of the second 70° 26' 17" N. The number of vibrations in a mean solar day at London being 86497·4, at Brassa they were 86530·507, and at Hare Island 86562·6386; giving an acceleration of 33·107 vibrations between London and Brassa, and of 32·1316 between Brassa and Hare Island; or 65·2386 between London and Hare Island.

XIX. On the correction of a pendulum for the reduction to a vacuum: together with remarks on some anomalies observed in pendulum experiments

The great importance which has, of late years, been attached to experiments on the pendulum, is evinced not only by the repeated and valuable labours of several of the most distinguished mathematicians and experimentalists of the present age, but also by the numerous scientific voyages that have been undertaken by several of the European Governments, with a view to ascertain and compare the results of different pendulum experiments made in various parts of the globe ; and thence to determine the true figure of the earth. These results, or the number of vibrations which are made in a mean solar day, whether made by the same, or by different pendulums, were considered, till within these few years, as strictly comparable with each other by means of certain well known corrections; whereby they were reduced 1° to arcs indefinitely small, 2° to a common standard of temperature, 3° to a vacuum, and lastly to the level of the mean height of the sea.