386 Mr H. Meikle on Compensation Pendulums, 



pared with the earth's motion of rotation, would continually 

 decrease; and therefore their centrifugal force, instead of 

 increasing with their distance from the earth's centre, must, 

 on account of the westward motion over the earth's surface, 

 decrease something like the centrifugal force of a comet while 

 receding from the sun. Indeed, if it observed the same law 

 in respect of the earth as the centrifugal force of a comet does 

 in respect of the sun, it could never become equal to the 

 attraction of the earth — being at first less, and always de- 

 creasing in the same ratio as that attraction does. But, with- 

 out pretending to assign the precise law of such decrease, or 

 of that of the centrifugal force of a current of air which pro- 

 bably soon spreads again towards the poles in the upper re- 

 gions, enough of it has just been noticed to set aside any 

 proof of a limit to the atmosphere, deduced either from the 

 refraction or the centrifugal force. 



Some plausible arguments of a very different kind were 

 advanced in the Philosophical Transactions for 1822, by the 

 late distinguished Dr Wollaston, to assign a limit ; but these 

 it will be unnecessary to discuss here, because they have been 

 completely disposed of by Dr Wilson, in the Transactions of 

 the Royal Society of Edinburgh, vol. xvi., p. 79. 



As to any solid shell which the late eminent mathematician, 

 M. Poisson, and others, have imagined to be frozen upon the 

 top of the atmosphere, and which is seriously referred to as 

 a reality, in various publications, it could scarcely fail to be 

 perceptible by its refracting and reflecting the rays of light ; 

 if, indeed, the dust which had been collecting on it for thou- 

 sands of years, would allow any light to reach us. None of 

 the other planets shew the least appearance of being enclosed 

 in any such shell. Nor would it better consist with the free mo- 

 tion of aeroliths and meteorites ; some of which are believed 

 to come from very remote regions, and could hardly be ex- 

 pected to treat such tender ware with sufficient delicacy. 



2. On Compensation Pendulums. — At the Manchester meet- 

 ing of the British Association, the late lamented Professor 

 Bessel brought forward some speculations regarding pendu- 

 lums, and called attention to certain circumstances which he 



