178 



On the Skin in the Bark Faces nf Mankind. [July 



v,hen still further heated. From this experiment and the preceding, he 

 wishes us to infer a power of vesicating in the sun's rajs not in proportion 

 to their temperature. 



In a third experiment, he exposf.d the backs of his hnnds to the sun 

 with a thermometer on each, the one hand being uncovered, while the 

 other had a covering of black cloth under which the thermometer waff 

 placed. After ten minutes, the degree of heat on each was marked, and 

 the state of the surface examined, and this was repeated three times. 

 During the last trial, the thermometer which had its ball covered by the 

 cloth stood at 106,** while the other was at 98.** The exposed hand wa* 

 scorched, that covered was unaffected in all the trials. I have not re- 

 peated this experiment because it is subject to an obvious fallacy, for the 

 ball of the thermometer being between the cloth and the part, a space 

 intervened, and ;icross this space the heat from the cloth could only pass 

 by radiation or by transmission through the thermometer, but not direct- 

 ly from the cloth to the hand, so that the heat might not accumulate on 

 the skin. 



In a fourth experiment, a Negro bore the sun's rays on his hand when 

 a thermometer on the part indicated 100^ without any scorching being 

 the result. As the scorching of which Sir Everard' speaks couid be only 

 a slight blush, it might not be observed on a sable skin. However, I do 

 not question the result of this experiment. 



Sir Everard observed in his next experiment, during the course of aa 

 eclipse, as the darkness on the sun's disk diminished, the scorching power 

 of the rays, concentrated by a lens,increased in a ratio which is assumed to 

 be greater than could be accounted for by the mere rise of temperature 

 during the time of the experiment. Whence it is to be inferi-ed that the 

 excess of effect is due to the increased quantity of light present with the 

 heating rays at each advance of time. A reference to the original paper 

 "will convince the reader that this assumption is established without 

 sufficient data. 



j\Iost stress has been laid by Sir Everard, and those who have adopted 

 his views, on the seventh experiment. We are told that, on the 9th of 

 September, at 11 A. M., thermometer 90° in the sun, the concentrated 

 rays applied to a piece of black kerseymere wrapped round the arm, gave 

 no real pain, as it is expressed, during 15 minutes ; and at the end of 

 that time left no appearance on the arm ; whereas, when white kersey- 

 mere was substituted, during the same time, and the concentration we 

 are led to suppose being the same, the heat of a thermometer in tlie suO' 

 only 86°, yet blisters were formed From this experiment, taken along 

 with those preceding, it is supposed to be fully proved that although 



