ACTION OF THE TROPICAL SUN. 



125 



Table VIII. — Gharacteristio records of experiments, etc. — Continued. 



JANUARY 28, 1911. 



Individual. 



Time. 



Arm. 



Cheek. 



Fore- 

 head. 



Neck. 



In hair. 



B. American, 

 brown hair — 



9.45 a. m. in shade 



9.50 a. m. exposed to sun„ 

 9.55 a. m. exposed to sun._ 

 10 a. m. exposed to sun ... 

 10.10 a. m. exposed to sun. 

 10.20 a. m. exposed to sun. 



32.5 



33.3 



33.9 



34.1 



33.1 



34.7 

 35.5 



35.7 

 36.9 



35.9 

 36.6 

 37.4 

 36.3 



35.5 

 36.4 

 35.9 

 35.6 



36.8 

 37.0 

 36.8 

 36.5 



39.1 

 38.9 



Or. Filipino, 

 dense black 

 hair. 



9.45 a. m. in shade 



9.50 a. m. exposed to sun.. 

 10 a. m. exposed to sun ... 

 10.10 a. m. exposed to sun. 

 10.20 a. m. exposed to sun. 



33.4 



34.0 



34.4 



34.2 



32.7 



37.2 

 37.2 

 36.1 



36.6 

 36.4 

 35.4 



35.9 

 35.9 

 35.2 



35.7 

 35.7 

 35.4 



43.4 

 44.0 



The figures given for pyrheliometer values are the number of milliamperes 

 necessary to produce the current which warms one German silver leaf to the 

 same temperature as the other exposed to the sun. They do not give absolute 

 figures (see discussion, p. 119), but they indicate thus far the relative value of 

 the radiation of the sun on the different days. Only clear days were chosen for 

 experiments, and but slight differences in the radiated heat of the sun were found. 



The temperature in the hair of an uncovered head increases to much 

 higher values than those of the skin, and here no fall is observed. The 

 color of the hair, as well as its thickness, is of great importance. In 

 the black, dense hair of a native of the Philippines, the temperature 

 may rise to 50°.l within one hour, and approximately 45° as a rule is 

 obtained within thirty minutes. 



Kunkel states that he has never observed skin temperatures above 

 35°. 5. In the tropical sun I have obtained slightly higher values, the 

 highest being 3 7°. 4, but generally 36°. 5 was the upper limit. 



Table IX shows a comparative study of the behavior of white and 

 brown skin. , In the sun, the white skin is always slightly hotter than 

 the brown and with the brown skin the fall in temperature after a 

 certain time of exposure is more pronounced. The heat absorbed by a 

 brown skin is greater than the heat absorbed by a white skin in the same 

 length of time. Therefore, it would seem as if the rise in temperature 

 should take place more quickly in colored than in white skin. This has 

 been experimentally proved to be true with dead skin by P. Schmidt ^^ 

 and Eykmann.^* Yet, just the reverse is true in li^dng men. BroA^oi 

 skm will absorb a greater quantity of rays than wbite, but being more 

 quickly heated, the point where sweat secretion begins is reached earlier, 

 and as soon as this point is reached the skin is cooled by water evapora- 

 tion. With the white skin, this process takes place more slowly and it 



''Log. cit. 



^'Firc/iotosArc/i. (1895), 140, 125-157. 



