Mr. J. Ivoiy on the Comtitution of the Atmosphere. 247 



that the heights in the atmosphere are ascertained with much 

 greater exactness than the temperatures, which are subject to 

 so many causes of irregularity. The great obstruction to our 

 knowledge of the constitution of the atmosphere is the want of 

 thermometrical experiments of a sufficient degree of exactness, 

 by means of which to correct and guide the determinations of 

 theor}'. 



Although the atmosph^-e determined by the equations (a) 

 agrees with nature as far as the observations in our possession 

 enable us to judge, yet this is proved only with regard to 

 altitudes that do not pass a certain limit. The total height 

 does not exceed 25 miles, which is probably less than half the 

 extent of the earth's atmosphere. Allowing therefore that the 

 two atmospheres coincide in their lower parts, yet they must 

 ultimately diverge greatly from one another. If instead of 

 taking m = 4, we make it 5, which is a supposition not in- 

 consistent with observation, the objection will still remain, 

 as the total height would be increased only to 30 miles. This 

 then is the objection to an atmosphere in which the decrease 

 of heat is proportional to the height, that the total altitude 

 does not quadrate with experience. The gradation of heat 

 that obtains in nature must therefore follow a different law 

 Accordmg to what has already been observed, there can be 

 no doubt that, as we ascend higher, the height requisite to 

 depress the thermometer one degree continually increases, 

 although the irregularity of the observations is so great as 

 to render it impossible to ascertain the rate of increase with 

 any tolerable precision. To illustrate this point, let us ao-ain 

 have recourse to the experiments recorded by Ramond, which 

 may be partitioned in two classes; one containing 16, in 

 which the height is less than 2000 yards; and the other 

 22 of greater altitude. The mean height for depressino- the 

 centigrade thermometer one degree deduced from the^first 

 class IS 144 metres or 78 fathoms; and the same height in 

 the other class is 180 metres, or 98 fathoms. The diflference 

 of these two determinations is considerable, and proves in- 

 contestibly a retardation of the decrease of heat in ascend- 

 ing. 



As we have it not in our power to determine upon sure 

 principles the relation that subsists between i and t in the at- 

 mosj^here, we can only make probable conjectures concernino- 

 It. Ihe most simple supposition is, that the two quantitiel 

 have always the same proportion to one another. Now, / be- 

 ing less than /, let us put 



/ = (l-/3)/; 



then, 



