Feb. 5, 1880] 



NATURE 



3 Si 



The additions to the Zoological Society's Gardens during the 

 past week include a Feline Dourocouli (Xyeti/ithecus voei/erans) 

 from Brazil, presented by the Right Hon. II. Hugh Childers, 

 M.P. ; an Ocelot (Felts fardalis) from British Guiana, presented 

 by Mr. G. Whilmore Christie ; a Little Grebe (Podice/s minor), 

 British, presented by Mr. Thos. Edward Frycc ; five Undulated 

 Grass Parrakeets (Melopsittacus undulatus) from Australia, 

 deposited ; a Black Lemur (Lemur macaco) from Madagascar, a 

 Tamandua Anteater (Tamandua telradactyla) from Brazil, 

 purchased. 



OUR ASTRONOMICAL COLUMN 

 Solar Parallax from the Velocity of Light. — Mr. D. 

 P. Todd, of the American Nautical Almanac Office, publishes 

 an intere.-ting note upon this subject. Remarking that the oppo- 

 sition of Mars in 1S62, when the planet approached near the 

 earth, and the experimental determination of the velocity of 

 light in the same year, mark the beginning of a new era in the 

 history of the determination of the solar parallax, he refers to 

 the many values of this constant w hich have since been worked 

 out, and the fact that although theoretically the better class of 

 these determinations should yield values in consistent harmony 

 with each other, there are at present singular and unaccountable 

 discordances. Prof. Newcomb's mean value of the parallax, 

 S"'84S, he observes, was regarded with caution only because it 

 was considered too small, the researches of Hansen, Leverrier, 

 Stone, and Winnecke appearing to place the parallax consider- 

 ably outside Newcomb's value. Within the last two or three 

 years, however, Mr. Todd remarks that " the parallactic pendulum 

 has sw ung quite to the lesser extremity of the arc until the true 

 value of the solar parallax has appeared possibly below S"'S, 

 and that, too, with good reason." But now there seems to be a 

 slight gravitation towards a central value, and he thinks it is not 

 possible to say that the mean equatorial horizontal parallax of 

 the sun i so much as the hundredth part of a second different 

 from the old figure, S" - 8i3 (27"'2 centesimal) adopted by La- 

 place in the Mecani,jue Celeste, and resulting from the early dis- 

 cussions of the transits of Venus in 1761 and 1769. 



Fizeau made the first experimental determination of the 

 velocity of light in 1S49, but the earliest which can lay claim to 

 the merit of trustworthiness is that of Foucault in 1S62, who 

 found it 298,000 kilometres per second, expressing confidence in 

 it to about one-six-hundredth part, though Mr. Todd estimates 

 the probable error tw ice as great. Next we have the first deter- 

 mination by Comu, detailed in the Journal dc Ilicole Polytcch- 

 nique, 1S74, which is 298,500 kil. =fc 1,000. The second deter- 

 mination by Comu, related in the Annates de I ' Obscmatoire de 

 Paris, t. xiii., 300,400 kil. ± 300 ; Helmert's rediscussion of 

 these experiments in 1876 assigns 299,990 kil., the probable error 

 of which value Mr. Todd estimates at 200 kil. Then follow two 

 determinations by Mr. A. A. Michelson, U.S. Navy, to the first 

 of which, 300,100 kil., he assigns equal weight with the earlier 

 value of Cornu ; the second, briefly described in the American 

 Journal of Science for November, 1879, Mr. Todd interprets, 

 giving equal weight to the one hundred separate determinations, 

 to imply a velocity of 299,930 kil. -fc 100. Assigning weights to 

 these various values, he finally deduces for the velocity of li'ht 

 299,920 kilometres, or 186,360 miles per second. 



The next step for the determination of the distance of the sun 

 from the earth is the combination of this value with astronomical 

 constants: (I.) Theory and observation of Jupiter's satellites afford 

 a result of the interval of time required by light in traversing the 

 mean distance of the earth from the sun, but there are only two 

 precise determinations of this interval, astronomically speaking ; 

 the first by Delambre in his Tables of the satellites, which was 

 also adopted by Damoiseau in his later tables, published in 1S36, 

 the second by M. Glasenapp, of the Observatory of I'ulkowa, in 

 1S74, from twenty-five years' observations of the first satellite of 

 Jupiter, ending in 1S73 ; the values are respectively 493 - 2s., and 

 5CW84S. + 1 -02s. ; the latter value rests upon a much smaller 

 number of observations than Delambre's, but Mr. Todd remarks 

 that it is difficult to form a just estimate of the w orth of an 

 average observation of an eclipse of a satellite of Jupiter in the 

 last century, and moreover, we have not the means of knowing 

 the process of discussion followed by the French astronomer ; he 

 combines the result by giving double weight to Glasenapp's 

 result, which depends upon observations of definite excellence, 

 discussed with modern precision, and thus adopts 498 - 3s. for the 



time-interval required for light to reach the earth Irom the 

 sun at her mean distance ; he then combines the distance thus 

 obtained with the value of the equatorial radius of the earth 

 derived by Listing ("Neue geometrische und dynamische Con- 

 stantendcsErdkorpers," Gottingen, 1878), and there results for 

 the mean equatorial horizontal parallax of the sun 8"'So2. 



(II.) The velocity of light, the constant of aberration, the 

 excentricity of the earth's orbit, and the earth's mean anomaly, 

 are connected by an equation w hich Mr. Todd employs for a 

 further determination of the solar parallax, adopting for the 

 constant of aberration Struve's value (2o"'445i), w ' tn Listing's 

 value of the earth's equatorial radius, and by this process the 

 sun's parallax is found to be 8"'8ll. Duly weighing the 

 probable variations of the elements which enter into these com- 

 putations, Mr. Todd concludes that the experimental deter- 

 minations of the velocity of light hitherto made, give, when 

 combined with astronomical constants, the meau equatorial 

 horizontal parallax of the sun = S"'SoS ± o''oo6, and hence the 

 corresponding mean radius of the terrestrial orbit = 92,800,000 

 miles. 



Faye's Comet.— Although, as lately remarked in this column, 

 the only known comet of short period which will be actually in 

 perihelion during the present year is that discovered by Prof. 

 Winnecke in 1858, Faye's comet will arrive at its least distance 

 from the sun in January, 1SS1, and may be observed during the 

 last half of 1SS0. Thanks to the admirable investigations of 

 Prof. Axel Moller, the theory of Faye's comet is known with 

 such precision that the ephemeris for the approaching reappear- 

 ance, which he communicated to the Swedish Academy in Sep- 

 tember, 1878, and which has been reproduced in the Astrono- 

 mische Nachrichten, may be expected to deviate in a very slight 

 degree only from the truth, and the comet's discovery will be 

 simply a test of the optical rapacity of the telescope. Prof. 

 Axel Moller commences his ephemeris on July 1, 1S80, and con- 

 tinues it to the end of the year. On July I the theoretical 

 intensity of light is o - 04, about equal to that at the date of the 

 last observation with the 15-inch refractor at I'ulkowa in 1844, 

 and the comet in about R.A. 23I]. 6m., Decl. + 8°, may be then 

 observable. The maximum intensity will be attained about the 

 middle of October, and will be about the same as at the last 

 observation in 1858 with the 9-inch refractor at Berlin, or 0'2I ; 

 at the end of the year the inten-ity of light will have diminished 

 to 0'I4. Thus the comet will be always faint, nor does it appear 

 likely to present itself under the favourable circumstances 

 attending its first appearance in 1S43 for several revolutions yet 

 to come. 



GEOGRAPHICAL NOTES 



By a postscript to the February number of the Geographical 

 Society's periodical we learn that a telegram has been received 

 from Mozambique, announcing the arrival of the East African 

 Expedition at Lake Tanganyika on October 28 ; the distance 

 from Lake Nyassa was found to be 250 miles, the country level, 

 and the people friendly. Mr. Thomson's account of his journey 

 from Dar-es-Salaam to Uhehe is given in the present num- 

 ber, and his notes of the route, though necessarily somewhat 

 rough, will afford useful material for filling up a blank in the 

 map of East Africa. We have also Mr. Wilfrid S. Blunt's 

 description of his visit to Jebel Shammar (Ncjd), and his journey 

 through Northern Arabia, of which he gave but an outline at a 

 recent meeting of the Society. The paper is illustrated by two 

 maps, one of which is a sketch map of Jebel Shammar furnished 

 by Mr. Blunt. Among the geographical notes is an interesting 

 account of Norwegian exploration last year in the Spitzbergen 

 seas, which appears to have hitherto escaped notice in this 

 country. Under the head of obituary we find brief notices of 

 Major Herbert Wood, R.E., and Mr. Hepworth Dixon, while 

 the remainder of the number contains the usual routine matter. 



According to the Colonics and India, Mr. Mitchinson, who has 

 travelled much among the natives of nearly all parts of Africa, and 

 especially in Berguela, Ovampo-, and Darnara-lands, &c, states 

 that he saw there wild beasts which had been tamed entirely by 

 the natives, although they are usually supposed never to attempt 

 it. On the River Cunene he found two perfectly tame cow 

 hippopotami, which were not confined in any way, but always 

 returned to the village. In a neighbouring place Mr. Mitchinson 

 also saw an African elephant which hid been tamed, and was 

 entirely under control. This certainly goes to show that the 



