112 GIBBS. 



While the darker skins absorb heat more rapidly, the radiation 

 is more rapid than from those of lighter colors and, since, in 

 full sun, the proportion of the body exposed is less than the 

 proportion in the shade, the darker-skinned races may for this 

 reason be somewhat better prepared to withstand the sun. 



In the sun, hair temperatures above 40° and a maximum of 

 50°. 1 are recorded. 



Gray-haired monkeys showed normal subcutaneous tempera- 

 tures in the shade and were quite comfortable, while in the sun 

 the temperatures rose above 48° and death ensued in less than 

 one hour and in one case in thirty minutes. 



White, gray, and black rabbits all die on exposure to the sun; 

 the black first, the gray next, and the white withstand the effect 

 longest. The subcutaneous temperatures do not rise as high as 

 in the case of the monkeys before death ensues. 



All measurements of temperature were made by means of 

 thermocouples and the subjects, men, monkeys and rabbits, were 

 protected from air currents. 



Clothing for human beings for protection from the sunlight, 

 should afford the greatest shade without obstructing air currents 

 carrying off evaporated moisture. The superiority of white 

 over colored materials as a reflector of the sun's rays is demon- 

 strated by the experiments with rabbits and a few measurements 

 under clothing. The ideal condition is attained by the shade 

 of a white umbrella lined with green cloth and supplemented by 

 as little clothing as possible. A broad brimmed, light weight, 

 white helmet, the band of which is so arranged that the frame 

 of the hat does not touch the head and allows the free passage of 

 air currents, is the best substitute for an umbrella. I can find 

 no justification for the heavy helmets. 



