1 82 1 .] Analyses of Books. 227 



Article XIV. 



Analyses of Books. 



Philosophical Transactions of the Royal Society of London for- 

 the Year 1821. Part I. 



This part contains the following papers : 



I. On the Black Rete Mucosum of the Negro, being a Defence- 

 against the scorching Effect of the Sun's Rays. By Sir Everard 

 Home, Bart. FRS. 



The author of this paper remarks, that to ascertain the use of 

 the black colour of the rete muc»sum in the negro has occupied 

 the attention of many physiologists. Sir Everard relates various 

 experiments which he performed to elucidate this curious sub- 

 ject. From these, I shall select two which indicate the most 

 remarkable differences in the power of the sun's rays upon white 

 and black skins. 



" I exposed," says the author, " the backs of my two hands 

 to the sun's rays, with a thermometer upon each ; the one hand 

 was uncovered, the other had a covering of black cloth, under 

 which the ball of the thermometer was placed. After ten 

 minutes, the degree of heat of each thermometer was marked, 

 and the appearance on the skin examined. This was repeated at 

 three different times. The 



1st time, the therm, under the cloth, 91° ; the other, 85° 

 2d 94 91 



3d 106 98 



" In every one of these trials; the skin was scorched that was 

 uncovered ; the other had not suffered in the slightest degree ;. 

 there was no appearance of perspiration on either hand." 



" The back of a negro's hand was exposed to the sun with a 

 thermometer upon it, which stood at 100° ; at the end of 10 

 minutes, the skin had not suffered in the least." 



Sir E. Home concludes from these and other experiments, 

 " that it is evident that the power of the sun's rays to scorch 

 the skin of animals is destroyed when applied to a black surface, 

 although the absolute heat, in consequence of the absorption of 

 the rays, is greater." This fact, the author informs us, was 

 explained by Sir H. Davy, by observing that " the radiant heat 

 in the sun's rays was absorbed by the black surface, and con~ 

 verted into sensible heat." 



II. On the Magnetic Phenomena produced by Electricity. In a 

 Letter from Sir H. Davy, Bart. FRS. to W. H. WoUaston* 

 MD. PRS. 



This paper is printed in the present volume of the Annals. 



1 q 2 



