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losophical world is indebted to M. Bessel for having first drawn the 

 attention of the public more immediately to this subject. For, al- 

 though Newton evidently suspected that such an influence existed, 

 and although the subject had been since fully discussed by the Che- 

 valier du Buat, nearly oO years ago, yet it does not appear that any 

 of the distinguished individuals, employed by the different Govern- 

 ments in making experiments on the pendulum in more recent times, 

 have had any notion that the effect of the air, on the moving body, 

 was any other than that depending on its density j and consequently 

 varying in amount according to the specific gravity of the metal of 

 which the pendulum might be composed. But M. Bessel has shown 

 that a quantity of air is also set in motion by the pendulum (varying 

 according to its form and construction), and thus a compound pendulum 

 is in all cases produced, the specific gravity of which will be much 

 less than that of the metal itself. M. Bessel's principal experiments 

 for establishing the accuracy of this principle, were made with two 

 spheres, about two inches in diameter, differing from each other very 

 considerably in specific gravity, one being of brass, and the other of 

 ivory, and each suspended by a fine steel wire. The author of the 

 present paper, however, pursued another and a very different course 

 for obtaining the same end : namely, by swinging the same pendu- 

 lum first in free air, and afterwards in a highly rarefied medium, 

 nearly approaching to a vacuum. From the difference in the results, 

 he deduces a factor (denoted by n), by which the old, and hitherto 

 received, correction must be multiplied in order to obtain the new and 

 more accurate correction indicated by M. Bessel; and which, in the 

 case of the two spheres above mentioned, is found by that author to 

 be equal to 1 95 . 



But Mr. Baily, instead of confining himself to spheres of this size, 

 and composed of these two substances only, has extended his inqui- 

 ries to pendulums of various magnitudes, substances and forms. His 

 first recorded experiment is on Borda's platina sphere, the diameter 

 of which is 1*44 inch; and he found that the old correction must in 

 this case be multiplied by 1*88 in order to obtain the true and accu- 

 rate correction ; or, in other words, that the old correction was but 

 little more than half what it ought to be. The author then tried 

 three other spheres of precisely the same diameter, but differing con- 

 siderably in specific gravity : namely, lead, brass, and ivory, all of 

 which gave nearly the same result ; the mean of the whole being 

 >i— 1 "86. He next proceeded to spheres of the size used by M. Bes- 

 sel, made of three different substances, viz. lead, brass, and ivory. 

 These gave a result (agreeing very well with each other,) somewhat 

 smaller than the former; the mean of the whole being n = \-/5 : 

 thus showing that the factor for the additional correction is due to 

 the form and magnitude of the moving body, and not to its weight 

 or specific gravity. This last value, as the author observes, differs 

 from that deduced by M. Bessel as above mentioned ; but the cause 

 of the discordance does not appear. 



The author then shows the effect produced on cylinders of various 

 kinds, both solid and hollow, and suspended in different ways, — on 



