58 BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



are the mean motions of the Earth, Mars, and Jupiter. This iuequality is remark- 

 able as being, if the work is correct, larger, and in the case of Mars very consi- 

 derably so, than any which arise from the simple perturbation of a single planet, 

 — the largest hitherto known in the case of the Earth amounting to only 715", 

 and in the case of Mars to 25 "5", Also, there will be a corresponding inequality 

 in the motion of the Moi-n, which I have not yet examined, but which may. per- 

 haps, be sensible; for, according to the investigations of M. Hansen, the inequality 

 in the motion of the Earth discovered by Prof. Air^-, amounting to 2-04:", with a 

 period of 240 years, produces one of not less than 23" in the motion of the Moon, 

 — so that, judging by analogy, there ought to be a sensible inequality in the pre- 

 sent case also. Again, there seems to be an inequality in the motions of Jupiter, 

 Saturn, and Uranus, wuh a period of somewhat more than 1,100 years, and 

 amounting in the ease of Jupiter to about 10" ; and in the case of Saturn to about 

 40", and in that of Uranus to 43". It arises from the fact, that 6 times the mean 

 motion of Saturn is nearly equal to twice that of Jupiter plus 3 times that of 

 Uranus. There are several others besides these, of less importance, arising fr-om 

 the product of two disturbing forces ; and there is even one which results from 

 the product of three forces, and appears to amount to nearly 1". There are also 

 several inequalities of the same kind in some of the asteroids, which are very 

 much larger than any in the motions of the principal planets; but as the theory 

 of the asteroids is considered to be of comparatively little interest, I have not 

 communicated them. 



But the most remarkable inequality of all of this kind is one which exists 

 in the motion of the comet of Encke, and which is due to the product of- the dis- 

 turbing forces of Jupiter and Saturn. The mean motion of this comet is very 

 nearly equal to 4 times that of Jupiter minus that of Saturn, or stated in other 

 n — 4w +Ji 



■words, is a very small quantity, — so that there will be a considerable 



n 

 inequality of the form P sin [nt — 4n t +n t +0), and also another of the form 



4 3 



P' sin {2nt — Sn t+2nt +6'). This latter term, I find, appears to account for at 



4. 5 



least a very considerable part of the remarkable acceleration which has been ob- 

 served jn the mean motion of this comet ; but owing to peculiar difficulties which 

 beset the question, I am not able to say whether it accounts for the wliole of it or 

 not. There will also be a remarkable inequality, arising from a similar cause, in 

 the motions of comets of short period. 



ox THE ELECTRIC FISHES AS THE EARLIEST ELECTEIC MACHINES EMPLOYED BY MAN- 



KIxXD. BY GEORGE WILSON, M.D., F.U.S.E., KEGIUS PROFESSOR OF TECHNOLOGY, 



UNIVERSITY OF EDINBURGH. 



"Were the question put to a circle of seientifie men, " With what form of electri- 

 cal apparatus were mankind first acquainted ?" we should be certain to hear much 

 ingenious discussion concerning tlie date of Von Kleist's earliest Leyden jar (1745), 

 Hauksbee's glass friction-machine (1709), and Otto Von Guericke's famous sulphur 

 ball (1670). Few however, would go further back than this primitive instrument, 

 unless the magnet were included among electrical apparatus, which in the form of 

 the compass-needle it cannot be; and even if we dignified with the name of instru- 



