THE STUDY OF TROPICAL SUNLIGHT. 19 



In the first ten to fifteen minutes the temperature of the 

 white skin rose more rapidly than the dark ; namely, an average 

 of 6°. 25 as against 2°. 60, but then the white skin began at a 

 lower shade temperature; and if the difference is taken into 

 account, the white skin rose 2*^. 79 as against 2". 60, so that there 

 is but little diflference in this respect. In the final temperatures, 

 one Igorot reached O'^.TS more than the American, while the other 

 was practically the same. 



In a second series of measurements, a Canadian, a Filipino, 

 and an American Negro were compared. The shade tem- 

 perature averaged 33^65, 33°.97, and 34°. 15, or higher by 0^63 

 to 3°. 59 than in the previous experiment. After thirty-one 

 minutes the Canadian reached 38°. 55, 37 '.40, and 38°.85; the 

 Tagalog and Negro, after tw^enty-nine minutes, reached 38°. 75, 

 38°.80, and 38°.78 and 39°.32, 38°.85, and 39°.15 respectively. 

 Therefore, the differences were +0°.20, +1°.40, and -0°.07 

 against the Tagalog and +0°.77, +1°.45, and 0".30 against the 

 Negro. In the first seven minutes the Canadian recorded a 

 rise of 4°. 3, 3°. 2, and 4°. 35; the Tagalog, in eight minutes, 5°. 55, 

 5°.40, and 5°.25; and the Negro, 3°.90, 3°.95, and 4°.50, so that 

 the temperature of the Tagalog rose decidedly more rapidly 

 than that of either of the others, but the Negro had an initial 

 shade temperature higher than those of the Canadian and Ta- 

 galog by somewhat more than 1°.0. The final temperatures, 

 therefore, are decidedly against the Negro, slightly so against the 

 Tagalog, and in favor of the Canadian as against the other two. 

 Taking these experiments into consideration and comparing 

 them with the indices we use in Manila, it may be said that, as 

 regards rise in temperature on exposure to the sun, the white 

 and brown skins are about equal, with a slight factor in favor 

 of the white, but that in the case of the very dark-skinned Negro, 

 the temperature on exposure reaches a decidedly higher point 

 than it does with either of the others. 



One fact very strikingly appears from these measurements, 

 namely, that the skin temperatures of all the subjects reach 

 higher points in the sunlight at the high altitude of Benguet 

 than they do in Manila, despite the lower shade temperature at 

 the former location. However, the measurements show that 

 perspiration begins at an earlier period in the lowlands. 



In explanation of the above results, it may be taken for 

 granted that the dark skin of the Negro will absorb heat more 

 readily than the light ones of the American or Canadian, but 



