258 PRINCIPLES OF VENTILATION. 



observations, it would follow that the causes assigned above foi 

 the gradual changes of temperature in a perpendicular column 

 of atmosphere, would apply to a state of temperature the very 

 reverse of the fact ; namely, that the higher the ascent, or the 

 more distant from the earth, the higher would be the tempera- 

 ture. Whether this reasoning be correct, or not, we think it must 

 be universally allowed that the fact has not hitherto received a 

 very satisfactory explanation. We conceive it to be one involv- 

 ing a new principle of heat ; by which we mean, a principle 

 which no other phenomenon of nature presents us with, and 

 which is not at present recognized as such. We shall endeavor, 

 in what follows, to make out that principle. 



The principle is this. The natural equilibrium of heat, in an 

 atmosphere, is when each atom of air, in the same perpendicular 

 column, is possessed of the same quantity of heat ; and, conse- 

 quently, the natural equilibrium of heat in an atmosphere is 

 when the temperature gradually diminishes in ascending. That 

 this is a just consequence cannot be denied, when we consider 

 that air increases, in its capacity for heat, by rarefaction ; and, 

 therefore, if the quantity of air be limited, it must be regulated 

 by the density. It is an established principle, that every body 

 on the surface of the earth, unequally heated, is observed con- 

 stantly to tend towards an equality. The new principle an- 

 nounced above would seem to suggest an exception to this law ; 

 but if it be thoroughly examined, it can scarcely appear in that 

 light. Equality of heat and equality of temperature, when 

 applied to the same body, in the same state, are found to be so 

 uniformly associated together, that we scarcely think of making 

 any distinction between the two expressions. No one would 

 object to the commonly observed law being expressed in these 

 terms. When any body is equally heated, the equilibrium is 

 found to be restored, when each particle of the body becomes 

 possessed of the same quantity of heat. Now the law, thus 

 expressed, is what I apprehend to be the true general law, which 

 applies to the atmosphere as well as to other bodies. It is an 

 equality of heat, and not an equality of temperature, that nature 

 tends to restore. 



The atmosphere, indeed, presents to us a strikingly peculiai- 



