84 Mr. J. Ivory on the Constitution of the Atmosphere. 



the result. The process seems to be a specimen of mental m- 

 genuity very slightly supported by facts, and corrected at every 

 step by calculations almost purely conjectural. But no ex- 

 perimental research could entirely fail in such able hands ; 

 and aldiough the Professor has not been successful in the prin- 

 cipal object he had in view, yet in another point he has added 

 to science, or at least to the rules for calculation. His for- 

 mula certainly does not accomplish what is the express pur- 

 pose of his research : it does not enable us to compute the 

 heat evolved when air is suddenly condensed, or absorbed 

 when it is suddenly rarefied. Thus it completely fails when 

 applied to correct Newton's calculation of the velocity of sound, 

 although it is now known that, in this instance, theory is suffi- 

 ciently reconciled with experiment, when a proper estimate is 

 made of the increased elasticity of air arising from the heat 

 disengaged by compression. What the formula does enable 

 us to compute, is the temperature at a height in the atmosphere 

 where the given elasticity prevails. According to Dalton this 

 temperature ought to be equal to the cold produced by an 

 equal rarefaction at the earth's surface. But here the hypo- 

 thesis of the philosopher of Manchester is at variance with 

 nature; for air rarefied at the earth's surface is colder, by 

 one part in four, than air of the same elasticity in the atmo- 

 sphere. 



Nothing certainly can be more reprehensible than to find 

 fault with the labours of others without explaining fully, and 

 proving clearly, the grounds on which the objections are 

 made. The practice of which I have ventured to disapprove 

 is not however uncommon in the present times ; and that I 

 may not furnish a new instance of it, I shall lay before the 

 reader the reasons of what has been advanced respecting Pro- 

 fessor Leslie's formula. Let I denote the length of the homo- 

 geneous atmosphere, equal to 4500 fathoms at the mean tem- 

 perature of 50° of Fahrenheit; x any height in the atmo- 

 sphere ; and 6 the relative pressure or elasticity of the air at 

 that height : then c being the base of the hyperbolic logarithms, 

 we obtain by what is usually taught in elementary treatises on 

 the supposition of a uniform temperature in the atmosphere, 



Consequently, }_ 



= c I 



and i V — ^ — I. 



by 



<, -=c ^ - c 



