November 1, 1898.] 



KNOWLEDGE 



213 



A remarkable increase (1200) in the number of cattle 

 killed by wild beasts in India is noted in the recent report 

 of the Chief C'oinniissiouer. This is due, according to 

 Sir Anthony Macdonnel, to the increasing scarcity of deer 

 in the jungle. The native huntsman, in bringing the 

 increasing resources of civilization against the deer, is 

 driving the tiger to trust to domesticated meat, whether 

 he prefers it or not. , , , 



Dr. Crochley Clapham, with the help of statistics, 

 would revolutionize our ideas of the " intellectual brow " 

 altogether. The smaller your head, and the more 

 prominent your occiput, the greater your sanity — at least 

 the mad have, as a rule, good heavy frontal lobes. Insane 

 heads, he also showed — and his statistics covered 4000 

 skulls — have a larger average size than sane. 



The question of the systematic abstracting and indexing 

 of scientific papers, to which we called attention in our 

 August issue, is under consideration by a committee of the 

 Eoyal Society. The need of the index is exemplified in 

 the current issue of the Philnsnpliiral Mafjit-.hv, where 

 Lord Kelvin notes too late that his communication upon 

 a piezo-electric pile repeats matter already published by 

 the brothers Cnrie in the Coiiijitcf: Ri-ndns in 1881. But it 

 will be very difficult to go behind the titles of papers, 

 which frequently do not indicate a tithe of the matters 

 referred to. ,^ , 



A remarkable mass of error, according to Dr. Hurst, 

 has grown out of an incorrect figure of the Berlin speci- 

 men of that most ancient of all birds, the Archceojitcry.i-. 

 Apparently three claws are shown in the position occupied 

 by the fila xpurin and manm of a bird's wing, but it has not 

 been noticed that the wing feathers could not have been 

 attached to these, but must have been fastened to another 

 digit, corresponding to the huge " ring finger " of a 

 Pterosaur, and which is still buried in the rock upon 

 which the cast lies. Yet, says Dr. Hurst, it is mainly 

 upon this fact that the tracing of the anjestry of birds, not 

 to the Pterosaurs but to the Deinosaurs, rests. 



LEXELL'S COMET AND THE QUESTION OF ITS 

 POSSIBLE IDENTITY WITH COMET V, 1889. 



By W. T. Lynn, B.A., F.R.A.S. 



THE first comet whose return was predicted did not 

 fail to appear about the time at which it was 

 expected. Not so, however, the second, which 

 was discovered by Messier in Paris on the 11th 

 of June, 1770, and calculated by Lexell to be 

 moving in an elliptic orbit of small eccentricity, which it 

 would require only about five and a half years to complete. 

 About a fortnight after its discovery it approached the 

 earth within a distance of only about six or seven times 

 that of the moon, and it was visible for a few weeks to the 

 naked eye. Its position at the return due in the winter 

 of 1775 was calculated to be such that it could not on 

 that occasion be visible ; but it was expected that another 

 return would take place in the summer of 1781, and that 

 the comet would then again be conspicuous. This ex- 

 pectation failed of fulfilment, and the erring body was 

 long known by the name of " Lexell's lost comet." Later 

 investigations, however, particularly those of Le Verrier, 

 have fully accounted for the failure, which was caused by 

 the powerful perturbing influence of Jupiter. To that 

 body we owe the comet's visibility in 1770, its orbit having 

 been altered by an approach to the giant planet of our 

 system in 17C7. But a much closer approach in 1779 

 (which brought the comet within a distance from the 



planet smaller than that of its fourth satellite) must have 

 so changed the orbit again that the comet would not be 

 visible to us at future returns, unless another approach to 

 •hipiter should reverse the efi'ect of this, and bring the 

 wanderer once more within the reach of our vision, tele- 

 scopic or otherwise. For more than a century at any 

 rate this did not take place ; but in 1889, on the 7th of 

 July, Mr. Brooks, of the Smith Observatory, Geneva, 

 New York, discovered a faint comet, which appeared to be 

 revolving round the sun in an elliptic orbit, with a period 

 of about seven years. Dr. Chandler's investigations 

 showed that this body must have made a very near 

 approach to Jupiter in 1886, so much so indeed as to 

 be nearer that body than any of its satellites, excepting, 

 pei-haps, the new tiny one discovered by Prof. Barnard in 

 1892, which is distant from Jupiter's surface by less than 

 the planet's diameter. The probability seemed on several 

 accounts to be great that Brooks's comet of 1889 was 

 identical with Lexell's of 1770, and that Jupiter in 1886 

 had reversed his work of 1779, and restored to us a sight of 

 the long-lost wanderer. Such a view appeai'ed probable, 

 but it would seem that it must after all be abandoned. 

 Dr. Poor, of the Johns Hopkins University, Baliimore, 

 I'nited States, has made a re-investigation of its 

 motions, availing himself of the principle formulated 

 by M. Tisserand, who succeeded the late Admiral 

 Mouchez as Director of the Paris Observatory last year. 

 This is, that whatever be the nature of the perturbations 

 produced in the elements of the orbit of a comet by the 

 attraction of a planet when the comet passes through the 

 sphere of its activity, one function will remain practically 

 unaltered. It is represented by the formula 



« = - + -oT .f/p cos. I, 



where n is the function in question, a, p, and i are 

 respectively the semi-axis major, the parameter, and 

 the inclination of the comet's orbit, and A and E are 

 the semi-axis major of the orbit of the disturbing 

 planet, and its radius vector at the point of the comet's 

 closest approach. Now, Dr. Poor has computed the 

 value of n with those elements of Brooks's comet which 

 correspond to the following four points of its path : 

 1st. March, 1881, the action of Jupiter insensible; 2nd. 

 March 24-5, 1886, entrance into the sphere of activity; 

 3rd. October 26-5, 1886, exit from that sphere; 4th. 

 September 30, 1889, the action of Jupiter again insen- 

 sible. These values of n, thus computed, are respectively 

 0'.5289, 0"5242, 0'5233, and 0-5294, showing the very 

 small change produced by so close an approach to the 

 planet as that which occurred in 1886. But the value of 

 n for Lexell's comet amounts to only 0-4852. This seems 

 to render its identity with Brooks's comet of 1889 ex- 

 ceedingly improbable, unless some considerable perturbation 

 had been produced by proximity to another planet besides 

 Jupiter, since the approach to that body in 1779. Saturn 

 is the only other planet which could come into consideration 

 in this respect, and Dr. Poor shows that the nearest 

 approach made by the comet to it took place between 1881 

 and 1884, and that even then the two bodies did not come 

 within five astronomical units of each other, so that the 

 resulting perturbations were quite inappreciable. With 

 the caution, however, of the true scientific mind, he 

 forbears to express himself decidedly against the conjectured 

 identity of Lexell's and Brooks's comets, but points out 

 that the question may be definitely settled at the expected 

 return of the latter in 1896. Meantime, he promises in 

 another paper (those here referred to, I should remark, are 

 contained in Nos. 302 and 303 of the Astmnoniirtil Journal) 

 to give the results of an investigation of the path of 



