380 Mr. Herapath on True Temperature, and the [Nov. 



more than counteracted by its absorption of oxygen. Many 

 other facts might be adduced which experience has taught us, 

 to show that, insalubrity depends chiefly on the humidity of the 

 air, and, therefore, most probably, on the absolute quantity of 

 vapour it contains. I do not mean to say that the unhealthiness 

 of air is exclusively due to its aqueous vapour. Probably other 

 matter which it releases in the violence of its efforts to evapo- 

 rate, and which consequently ascends with it, or most likely 

 adheres to its particles, forms a more pernicious element than 

 pure vapour alone. With this view we should still say that in 

 any particular place the unhealthiness of the air depends on the 

 absolute quantity of its vapour ; but on comparing the airs of 

 different places, we should conclude, that the insalubrity depends 

 conjointly on the absolute quantity of vapour and the quantity 

 and inimicability of the other matter it contains. Hence one 

 reason why the vapour, and, consequently, the atmosphere, of 

 the sea may commonly be more healthy than that of the land ; 

 for the vapour raised from the sea is most probably more faithful 

 to the pure constituents of water, oxygen and hydrogen, and 

 much less contaminated with extraneous matter than the vapour 

 raised from the land. The breeze, however, which usually pre- 

 vails on sea, by incessantly changing the air we breathe, and 

 carrying off any noxious exhalations, constitutes no immaterial 

 part of its healthiness. By these views we see also why one 

 place shall be so uniformly healthy, and another so uniformly 

 unhealthy ; and why a place which is equally cold, equally high, 

 and equally dry, with another, shall, notwithstanding, be less 

 friendly to the human constitution ; for other things being the 

 same, the salubrity of the air depends on the soil which gives 

 birth to its vapour. Supposing, however, a perfect equality in 

 other matters, phenomena appear to me to mark aqueous vapour, 

 however pure it may be, as by no means beneficial to health. If 

 this be the case, it will remain for philosophers to determine in 

 what this pernicious principle consists, and the mode of its opera- 

 tion. Judging from the nature of the elements of vapour, I should be 

 disposed to attribute it to the hydrogen. But this is little more than 

 mere conjecture. Oxygen itself, combined with hydrogen, in the 

 form of vapour, may be, perhaps, as inimical to the human constitu- 

 tion as hydrogen or nitrogen alone. Speculations of this kind, how- 

 ever, belong not to the mathematical but the medical philosopher. 

 I have gone a little out of my way for the sake of exciting among 

 those, in whose province it more immediately comes, successful 

 inquiry into a subject which is of the utmost importance to man- 

 kind. Whether my views are deserving attention, and my 

 wishes shall be seconded by the efforts of others or not, can be 

 to me, as an individual, but of little consequence. The motives 

 which prompted me to deliver my sentiments on this subject flow 

 from an idea, which has ever appeared to me to form the true 

 estimate of human attainments and discoveries ; namely, that 



