THE DISCOVERY OF SATELLITES OF MARS.

Samoa Times and South Sea Gazette, Issue 17, 26 January 1878, Page 2

THE DISCOVERY OF SATELLITES OF MARS.

OHO of the most wonderful astronomical discoveries of the present century was made in August last, by Professor Asaph Hall, of tho United States Navy, at Washington. Our readers will remember a telegram being received in the Australian Colonies some weeks ago, from tho Astronomer Royal, requesting the astronomers hare to " keep a watch on Mars for suspected satellites." Wo have now been favored by Mr. C. Todd, C.M.0., with the sight of a copy of a letter to the Hon. It. W. Thompson, Secretary of the United States hairy, announcing the discovery. It was as follows :—" U. S. Naval Observatory, Washington, August 21, 1877 Sir.--The outer Satellite of Mars was firs; observed bv Professor Asaph Hall, U. S. N., oil the night of the 11th of August. 1877. Cloudy weather prevented the certain recognition of the true character at that time. On August lli, it was again observed, and its motion was established by observation extending through an interval of two hours, during which tho planet moved over .'SO seconds of arc. The inner satellite was first observed on the night of August 17, and was also discovered by Professor Hall. On Saturday, August 18, the discoveries were telegraphed to Alvan Clark, ami Sons, Canibridgeport, Mass., in order that if the weather should be cloudy at Washington, they might confirm th-cxi.-tellce of the satellites with the 20-inch telescope of Mr. McComiick, which is in their hands. The discovery was confirmed by Professor Piokcring and his assistants at Cambridge, Mas-., and by the Messrs. Clark, at Cambridgeport. On August IS), the discovery wi s communicated to the Smithsonian Institution, by which it was announced to the American ami European Observatories, in the following dispatch : —" Two satellites of Mars discovered by Hall, at Washington. First, elongation west, August In. 11 hours, Washington time. Distanc.

80seconds. Period, 30 hours. Distami of second, 50 seconds." It will be sw-n hereafter, that the statement nt' ,">(i seconds as tin; distance of the inner mi' was erroneous. A series <•■!' iiiiutit--observations extending I'rom August II to 20, are given, but being strictly scientific need not lie repeated here. Tieletter is signed "John Rodgei*, RunAdmiral and Superintendent." We haw some further particulars in the San Francisco papers. At first Professor Hall scarcely credited the great discovery he had made, but tlie next, day he enmmunicatcd the result of his observations to Professor Neweomh, who felt so confident that the new star was a satellite of Mars, that he triado a rough calculation of the time of its revolution round th« planet, which he estimated at from :>() to :I2 hours. On this estimate the satellite was again watched for, and it appeared, true to tile time, emerging from behind the planet with another satellite in company. Professor Hall was now satisfied of the nature of his discovery, ami communicated it officially to Admiral Roflgors, the Superintendent. Further observations by other astronomers in America confirmed the fact of Mars having at least one satellite, and tindiscovery has been telegraphed to the European observatories. The existence of the second satellite is not looked upon as ascertained beyond all duubt, but it is confidently believed to he the case. Tho extreme brillancy of this planet has rendered it necessary to allow it to pass out of the field of the telescope for the better observation of the satellite. Mars is much nearer to the earth than it has ever boen, being only about 34 millions of miles distant. The distance of the first satellite from the planet is estimated at between 14,000 and 10.000 miles, while that of the second is somewhat less. The first is a faint object about the sizo of a star of the 18th and 14th magnitude, and the second is supposed to° be not more than between 50 and 100 miles in diameter. Up to the present time nothing bus been seen at Melbourne or Adelaide Observatory of cither of the Satellites, The power of our telescope is, however, vastly inferior to that in tho American Observatory. Mr. 1). P. Todd, of the United States Naval Ohservatorv, Washington, who forwarded to MY Charles Todd, C.M.G., of the Adelnide Observatory, tho copy of the letter announcing the discovery of Satellites of Mars, writes to him under date, August :!!>, ns follows:—'• Dear Sir—Allow life to j thank you for the very valuable, scries of observation! of Jupiter's Satellites which you succeeded in making last year. I may express myself us especially glad that astronomy has secured an observer in your part of the globe so diligent in this particular Bold of research. The locution of your observatory ndds, of course, an especial value to this sort of work which you have undertaken in so systematic u manner. If you had tho good fortune to observe the eclipse of the fourth sat) llite on the 28th instant, may I ask of you the favor of a note bearing the observed times and other particulars,

as noon as your other engagement* will permit 1 The appropriate time (to tho nearest three or four second*, will mnr niy purpose surfukiitly. Tin; very serious deficiency of observations of this satellite darkens considerably the prospect of the much-needed" new ■ecliptic tables. 1 take much pleasure ill mailing to you with this note a eopv of my continuation of J)e Damoiseau'a t-ibles. ecliptiques, ,v.<\ ; al>o a oopy of the ollicial letter respecting Satellites ot Man. I am, dear Sir, yours very truly, IV P. Todd."—"South Australian Advertiser.''