Skin in the Dark Baces of Mankind, 381 



lowed to remain for five or at most seven minutes, produced 

 blisters. During the same period very little apparent effect 

 followed the application of the white cloth, though consider- 

 able pain was sometimes produced. The experiment was at 

 different times performed on several individuals, all of whom 

 found the black cloth give the sensation of pain sooner than 

 the white. On the whole, I found nothing like the difference 

 described by Sir Everard, though certainly the vesicating ef- 

 fect of the black surface appeared to be much greater than that 

 of the white. From many experiments I conclude, that the 

 rays of the sun will scorch when they are applied to the 8Ui*» ' 

 face so as to cause a heat of about 130° and upwards. And 

 from the experiment related by Sir Everard, it appears that 

 hot water is capable of producing a similar effect at that tem- 

 perature. From all this, I am inclined to deny the existence 

 of a scorching power in the sun's rays, independent of the heat 

 they contain, or at least of the effect they produce on the ther- 

 mometer. Moreover, if such a power do exist, black cloth 

 should yet scorch more than white, since it will absorb all the . 

 rays of light, whereas the other surface will reflect tiiem. "^'*^ 



In those experiments which I performed, care was taken to 

 have the white and black cloth nearly of the same density. Sir 

 Everard does not appear satisfied with his explanation of the 

 extraordinary yac^ he relates, for he gives another furnished by 

 Davy, who, indeed, is made to ascribe the alleged difference in 

 vesicating power between black and white surfaces, to the for- 

 mer rendering the heat sensible. Were I not quoting from the 

 Philosophical Transactions, a misprint might be suspected. I 

 conclude that a black skin will absorb more heat than a white 

 skin, and were it not for other accompanying circumstances, 

 would produce inconvenience precisely in the ratio of the amount 

 of heat absorbed. It must not be overlooked, however, that in 

 the Negro the pigment is not superficial, but covered by a 

 layer of translucent cuticle. The experiments of Dr Stark 

 prove that colours absorb heat in proportion to their depth of 

 shade through transparent media. It only remains to shew 

 the cuticle to be a medium in the condition of those. For 

 this purpose, I covered the balls of a differential thermometer, 

 one witli cuticle, the other with cuticle of the same thickneaSy 



VOL. XXIX. NO. LYIII. — OCTOBER 1840. * C C 



