216 iiiSToriY OF 



unite *11 the ir properties, being invigorated by tlie weif^ht of the 

 air, relaxed by its moisture, enfeebled by its heat, and stiH'ened 

 by its frigidity.* 



But it is chiefly by the predominanee of some peculiar vapour, 

 that the air becomes unfit for human support. It is often found, 

 by dreadful experience, to enter into the constitution, to mix 

 with its juices, and to putrefy the whole mass of blood. The 

 nervous system is not less affected by its operations ; palsies and 

 vertigoes are caused by its damps ; and a still more fatal train 

 of distempers by its exhalations. In order that the air should 

 be wholesome, it is necessary, as we have seen, that it should 



* It is surprising the degree of heat the human body is capable of bearing. 

 This seems to be nmnected with the action of the skin, and no doubt depend, 

 ing upon it ; for the liumaii body evidently has the power of bearing a very 

 high temperature, without any change in tlie temperature of the body itself. 

 Accurate experiments upon this subject (for it is needless to mention the in- 

 accurate trials of Boerhaave) were first made by M. Tillet, at Paris, in HGi 

 The suljject was resumed by Dr Fordyce, in 1775, and there are two curious 

 papers in the Philosophical Traubactions, giving an account of the pheno- 

 mena which were observed. Dr Foi dyce heated a room by means of flues 

 running along the ftoor, and by means of boiling water, to the temperature of 

 about liOo ; he then stripped himself to the shirt, and went into the room. The 

 temperature of liis body continued at about UK)", but his pulse increased con. 

 siderably in rapidity, beating 126 times in a minute. Streams of water con- 

 densed upon his body, and ran down to the floor. This was the vapour of the 

 hot water by means of which the room was heated, condensed by the action 

 of the comparatively cold surface of his body. Dr Fordyce invited the Hon. 

 Captain Pliipps, Sir Joseph Banks, Dr SoUinder, and Sir Charles Blagden, 

 to repeat and verify these experiments. These gentlemen attended two 

 several days, and during the last of these days there were also present Lord 

 Seaforth, Sir George Home, Mr Dundas, and Mr Nooth The room was 

 heated by means of a large iron code placed in the centre, and heated red 

 hot. The thermometer, in some of their trials, rose to 260*. This degree of 

 heat they found they could bear for a considerable time without any great in- 

 convenience, both when dressed and when naked. The temperature of the 

 hody continued at 100», the pulse was greatly quickened, increasing to 14-1 

 beats in a minute. The perspiration was very violent, and, no doubt, 

 together with the imperfect conducting power of air, occasioned that 

 equability of temperature which the body preserved. To prove that the heat 

 of the air was really as great as they stated, and that there was no error in 

 their thermometer, they introduced eggs and beaf-steaks, which were per. 

 fectly roasted in a short time. Water introduced, remained stationary at 

 1400, the evaporation preventing any farther increase; but when this eva- 

 poratidn was stopped, by covering its surface with oil or melted wax, the 

 water si'on heated so as to boil briskly. Experiments attended with nearly 

 a similar result, were made at the same time by Dr Dobson, at Liverpool. 



