VOL. LXV.] PHILOSOPHICAL TRANSACTIONS. 697 



our clothes in enabling us to bear such high degrees of heat. With this view I 

 took off my coat, waistcoat, and shirt, and in that situation went into the room, 

 as soon as the thermometer had risen above the boiling point, with the precau- 

 tion of holding a piece of cloth constantly between my body and the cockle, as 

 the scorching was otherwise intolerable. The first impression of the heated air 

 on my naked body was much more disagreeable than I had ever felt it through 

 my clothes ; but in 5 or 6 minutes a profuse sweat broke out, which gave me 

 instant relief, and took off all the extraordinary uneasiness : at the end of 12 

 minutes, when the thermometer had risen almost to 220°, I left the room, very 

 much fatigued, but no otherwise disordered; my pulse made 136 beats in a 

 minute. On this occasion I felt nothing of that oppression on my breath, 

 which became so material a symptom in the experiment with my clothes when 

 the thermometer had risen to 26o° : this may be partly explained by the less 

 quickness of my pulse, the difference being at least 8 beats in a minute, and 

 probably more, as in the experiment without my shirt the pulsations were 

 counted before I had left the room ; but there is a further circumstance to be 

 taken into consideration, that the experiment attended with oppression on the 

 breath was made in the evening after a very plentiful meal, whereas the other 

 was made in the forenoon, some hours after a moderate breakfast. The uimsual 

 degree of fatigue which I felt from the experiment without my shirt, must be 

 ascribed in great measure to the more violent eflfbrt which the living powers were 

 obliged to exert, in order to preserve the due human temperature, when such 

 hot air came into immediate contact with my body. In the present case it ap- 

 pears beyond all doubt, that the living powers were very much assisted by the 

 perspiration, that cooling evaporation which is a further provision of nature for 

 enabling animals to support great heats. Had we been provided with a proper 

 balance, it would undoubtedly have rendered the experiment more complete, to 

 have taken the exact weight of my body at going into, and coming out of, the 

 room ; as, from the quantity lost, some estimate might be formed of the share 

 which the perspiration had in keeping the body cool ; probably its effect was very 

 considerable, but by no means sufficient to account for the whole of the cooling, 

 and certainly not equable enough to keep the temperature of the body to such 

 an exact pitch : for it should here be remarked, that during all the experiments 

 made this day, whenever I tried the heat of my body, the thermometer always 

 came very nearly to the same point ; I could not perceive even the small differ- 

 ence of 1 degree, whieli was observed in our former experiments. Should these 

 considerations however be thought insufficient to prove that evaporation was not 

 the sole agent in keeping the body cool, I believe that Dr. Fordyce's experiments 

 in moist air will be found to remove all doubts on this subject Several of the 

 gentlemen present, as well as myself, went into the room without shirts many 



VOL. XIII. 4 U 



