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On the Limits of the Atmosphere, and on Compensation Pen- 

 dulums. By Henky Meikle, Esq. Communicated by the 

 Author. 



1. On the Limits of the Atmosphere, — ^Various attempts 

 have at different times been made to prove that the atmo- 

 sphere of the earth is not only finite, but of comparatively 

 small extent ; and there are some methods of reasoning which 

 have been long regarded as quite conclusive, in assigning 

 limits beyond which the atmosphere could not possibly ex- 

 tend. None of these, however, though they afford consider- 

 able probability, can be said completely to demonstrate the 

 thing. But without at all meaning to contend for the inde- 

 finite extent of the atmosphere, I shall briefly state some 

 doubts regarding one or two of the most usual modes of as- 

 signing its limits. 



As to any evidence which the refraction may be supposed 

 to afford, I need only observe that such an idea, in a great 

 measure, assumes the thing to be proved. It assumes that 

 a limit exists, and thence infers where the limit is. For, did 

 the density of the air decrease till at a certain distance, and 

 then become uniform, the refraction could at best point out 

 where the uniform density commences ; because the refrac- 

 tion would have nothing to do with the air, which was uni- 

 form. 



Neither does any proof, derived from the centrifugal force 

 of the rotation of the atmosphere, seem more to the purpose ; 

 because it depends entirely on the assumption that the earth 

 and its atmosphere revolve together in one rigid mass in the 

 space of a sidereal day : whereas, there is reason to think 

 that the higher parts of the atmosphere, especially about the 

 equator, revolve more slowly than the lower, or than the 

 earth's surface does. For if, as is generally admitted, the 

 principal motions of the air between the tropics, are from the 

 south-east and north-east towards the equator, where they 

 unite in one current whose particles move botli westward and 

 upward, the case will be very difi'erent ; because the angular 

 motion of such particles round the earth's centre, or com- 



