VOL. LXXVIII.] PHILOSOPHICAL TRANSACTIONS. 489 



mation, or are produced afterwards in the gradual evolution of an animal. This 

 does not appear to be a question of much importance; nor perhaps can it be ab- 

 solutely determined. But on the whole it is more reasonable to think, that the 

 same plan of formation is continued from the beginning, than that at any sub- 

 sequent period there is a change in that plan. It may be observed, that it is 

 exactly the same creative action which produces the natural structure, or any de- 

 viation from it; for in cases of deviation the action is either carried too far, 

 ceases too soon, or is diverted into uncommon channels. This will explain 

 the various kinds of monstrosity from redundancy, deficiency, or transposition 

 of parts. 



XXII. On the Georgian Planet and its Satellites. By IVm. Herschely LL. D., 



F. R. S. p. 364. 



In a paper, containing an account of the discovery of 2 satellites revolving 

 round the Georgian planet, Dr. H. gave the periodical times of these satellites 

 in a general way, and added that their orbits made a considerable angle with the 

 ecliptic. The most convenient way of determining the revolution of a satellite 

 round its primary planet, which is that of observing its eclipses, cannot now be 

 used with the Greorgian satellites; and as to taking their situations in many suc- 

 cessive oppositions of the planet, which is also another very eligible method, that 

 must of course remain to be done at proper opportunities. The only way then 

 left, was to take the situations of these satellites, in any place where they could 

 be ascertained with some degree of precision, and to reduce them afterwards by 

 computation to such other situations as were required for the purpose. In Jan. 

 Feb. and March, 1787, the positions were determined by causing the planet to 

 pass along a wire, and estimating the angle a satellite made with this wire, by a 

 high magnifying power. But then he could only use such of these situations 

 where the satellite happened to be either directly in the parallel of declination, or 

 in the meridian of the planet; or where, at least, it did not deviate above a few 

 degrees from either of them; as it would not have been safe to trust to more 

 distant estimations. 



In computing the periods of the satellites Dr. H. contented himself with syno- 

 dical appearances, as the position of their orbits, at the time when the situations 

 were taken from which these periods are deduced, was not sufficiently known to 

 attempt a very accurate sidereal calculation. By 6 combinations of positions at 

 a distance of 7, 8, and Q months of time, it appears that the first satellite per- 

 forms a synodical revolution round its primary planet in 8*^ 17^ 1"" and 19;3^ 

 The period of the 2d satellite deduced likewise from 4 such combinations, at the 

 same distance of time, is IS*^ 11^ 5"" and 1.5^ The combinations of which the 

 above quantities are a mean do not differ much among themselves; it may there- 



VOL. XVI. 3 R 



