4io Why mo'ift Air gives the So/alien of Cold. [Book V. 



The eudiometer is a good teft of air as far as re- 

 gards the diminution of the oxygenous part} but it is 

 on the whole an imperfect inftrtiment, as it affords no 

 means of diftinguilhing the deleterious vapours with 

 which the atmofphere may occafionally be charged. 



Befides their deleterious properties, the mixture of 

 watery particles and vapour in air has alfo confiderable 

 tffect with refpeft to its power of conducting heat 

 from our bodies. The rarity or denfity of air feems 

 to have little effect with refpect to its conducting 

 power, which indeed appears entirely to depend on 

 the quantity of moifture it contains. A moift air con- 

 ducts heat with much greater rapidity than a dry air. 

 Whence (fays the ingenious Count Rumford) c I can- 

 not help obferving with what infinite wifdom and 

 goodnefs, Divine Providence appears to have guarded 

 us againft the evil effects of exceftive heat and cold in 

 the atmofphere j for were it pofTible for the air to be 

 equally damp during the fevere cold of the winter 

 months, as it fometimes is in fummer, its conducting 

 power, and confequently its apparent coldnefs, when 

 applied to our bodies, would be fo much increafed by 

 fuch an additional degree of moidure, that it would be- 

 come quite intolerable i but, happily for us, its power 

 to hold water in folution is diminifhed, and with it its 

 power to rob us of our animal heat, in proportion as its 

 coldnefs is increafed. Every body knows how very 

 difagreeable a very moderate degree of cold is when 

 k is very damp; and hence ic appears, why the ther- 

 mometer is not always a juft meafure of the apparent 

 or ienfible heat of the atmofphere. If colds or ca- 

 tarrhs are occafioned by our bodies being robbed of 

 our animal heat, the reafgn is plain why thofe diforders 

 prevail moft during the cold autumnal rains, and upon 

 the breaking up of froft in the Ipring. It is like wife 

 5 plain, 



