DoBrlne of Huat, with refpeSl to denfe and tlaJHc Fluids* , f j^ 



fimilar dccompoGtion In the evaporation of other bodies lefs confpicuous. The vapour of 

 ether, according to Lavoifier's experiments (Mem. de I'Ac. des Sciences, 1780) becomes, by 

 the mere admiiTion of common air, a permanently eladic fluid, and in this ftate deflagrates 

 on the application of flame, like a mixture of oxygen and hydrogen gafes. The very in- 

 terefting experiments of the Dutch chemifts on the decompofition of alcohol and ether, in 

 the paflage of their vapours through tubes of glafs or of porcelain, may be confidered as 

 affording evidence to the fame general purport. 



In anfwer to the other part of the objeftion, that if fubftances be confidered as decom- 

 pofed in evaporation, their parts fliould efcapc fucceffively, according to their different 

 affinities for caloric, and not altogether, as is the cafe, it might be fufficient to obferve, 

 that the efcape of one from the remainder in an uncombined ftate, all our obfervations of 

 other phenomena teach us that this ftate muft neceffarily be that of an elaftic gas, and 

 therefore the aeriform converfion of both parts muft take place together. But we may go 

 further, and affirm that it is to the phenomena, as thus explained, that we muft have re- 

 courfe, in order to underftand one of the moft important ^nd diftinguiftiing circumflances 

 by which the procefs of evaporation is marked. I mean the generation of cold. And if 

 this can be {hewn, the theory which I have been attempting to explain will have fomething 

 more than analogy for its fupport. 



ftate In the atmofphere. Yet he feems to have formed his idea of it as " a permanent gas, unchangeable, 

 " like other compounds, except by an eleftive attraftion fuperior to that which unites its ingredients,'* 

 page 368. And in this light we cannot wonder at his exprefling his inability to explain " what occafions 

 *' the formation of water in the air, to admit of its falling in rain at any time." Without profeiling to enter 

 at all into the rationale of this phenomenon, I may obferve that the principal difficulties with which it feems 

 embarrafled in his theory will be removed, if we coniider water to enter Into the atmofphere, not as ^per- 

 ixanent compound gas, but as decorapofcd into the two original permanent gafes belonging to its conftitution. 

 Thefe, having diffeient fpecific gravities in the atmofphere, muft be fuppofed to occupy diflferent regions 

 in the atmofphere, which, however, will vary, and occafionally intermingle with each other by tlie operation 

 of different circumftances. In fuch cafes the affinity between their refpeflive bafes, when aided by any oc- 

 currence difpofmg them to part with the caloric wluch feparates them, may be eafily fuppofed to occafion 

 a re-union. 



According to this author's idea of the air proceeding from the evaporation of water b«>ng a permanent gas,/ 

 to what can he affigii its fpecific diftinftion from water itfelf ? Will he Ciy In Its combination with caloric ^ 

 But he has fliown that it is botli producible without the afliftance and Irrefolvible by the fubtraftion of caloric. 

 Befides, we have pofitlve evidence that this gas, in its original ftate, Is not permanent. The vapour im- 

 mediately rifmg from boiling water is this gas In its original ftate, tranfparent and elaftic. But It will not 

 be faid that this is incondenfable by cold. It becomes permanent only by the local feparatlon of its parts. 

 And if we admit this feparatlon, I think we not only fee the arguments which the author has brought to- 

 gether to illuftrate the modifications of the atmofphere by evaporation in aftronger light, but we fee thp 

 analogy of feveral other modifications with the feme general fource. We fee in particular why a greater ^ 

 quantity of oxygen is obferved in the atmofphere during dry ferene weather than during the prevalence of 

 -clouds, fogs, or raln-S} and, connefled with this, why the air of lower regions has been always fownd 

 charged with mere oxygen than that of more elevated ones, 



it 



