82 Mr. J. Ivory on the Constitution oj I he Atmosphere. 



there are no circumstances connected with these facts, except 

 what we have mentioned, it seems to be impossible to account 

 for the heat which disappears from the thermometer in the 

 one case, and again becomes sensible in the other, unless we 

 suppose that it enters into combination in a latent form Avith 

 the dilated air, and is again evolved when the same air reco- 

 vers its former volume. So far we may allow that Dalton has 

 reasoned rightly with regard to the decrease of heat in the 

 atmosphere; but, as we may form innumerable hypotheses 

 connecting the variations of temperature with the changes of 

 density, the principal object of research remains in a manner 

 untouched. 



Professor Leslie has adverted to this subject in the article 

 Climate in the Supplement to the Encyclopcedia Britannica. 

 He explicitly adopts the theory of Dalton, although he has 

 not mentioned the author from whom he borrowed it. The 

 demonstration he has attempted is certainly not much to the 

 purpose*. In whatever way we account for the constitution 

 of the atmosphere, we must conceive that there is a mean state 

 about which it makes small oscillations on opposite sides. In 

 a stratum of air at a given height above the eartli's surface, 

 the heating and cooling causes will balance one another in a 

 length of time, and the mean temperature will be invariable. 

 But this gives us no information concerning the law of tem- 

 perature in passing from one stratum to another. While the 

 mean temperature of each stratum remains constant, the gra- 

 dation with respect to the different strata, may be infinitely 

 varied. The theory of Dalton has nothing to do with incre- 

 ments and decrements of heat received at different times, and 

 finally compensating one another ; it is founded on a property 

 inherent in air, according to which the temperature of any 

 given mass is determined by the dilatations and condensations 

 it is made to undergo. 



2. Leaving general arguments, let us inquire what light will 

 be thrown upon this subject by the knowledge of the condi- 

 tion of the atmosphere that has actually been obtained. And 

 here all our information is derived from one source, namely, 

 the measurement of heights by the barometer. Fortunately 

 great pains have been taken to perfect this method, which has 

 been extensively applied by many careful observers. We are 

 thus enabled to compare the temperatures and pressures de- 

 termined by actual observation at many different elevations. 



Ramond, in his work on the barometrical formula, has col- 

 lected 42 diffei'ent measurements, for the express purpose of 



* Stippt, Enci/clopcedia BrUannica, vol. iii. [). 185. 



ascertainino; 



