INFLUENCE OF PHILIPPINE CLIMATE ON WHITE MEN. 



433 



Comparing the average number of hours of sunshine with the figures for certain 

 places in the United States it will be found that Manila receives 51 per cent 

 of the theoretical sunshine while New York receives 56 per cent, Chicago 57 per 

 cent, Denver 69 per cent, and Santa Fe 76 per cent. (D In other words numerous 

 regions in the temperate United States are characterized by many more hours of 

 sunshine than are the tropical Philippines. These figures of course do not take 

 into consideration the question of intensity of the sunlight in the two zones. 



The quantity of watery vapor in the atmosphere has a direct infiuence on the 

 climate, because it checks to some extent the radiation of heat, and the relative 

 humidity is of still greater importance in studying the influence of climate on 

 man because the greater the humidity the more marked is the interference with 

 the thermolysis of the body resulting from the evaporation of perspiration. (21) 

 The following table shows the monthly and annual averages in Manila for a 

 period of twenty years. These figures may be compared with average relative 

 humidity records for July of 70.6 per cent for Chicago, 70.4 per cent for New 

 York, 71.0 per cent for Washington, and 72.3 per cent for New Orleans. 



Table IV.— 



■Monthly and annual averages o 



f relative humidity 



in Manila, 



oer cent. 



1 

 Jan. ' Feb. ! Mar. 

 i 



Apr. 



May. 



June. 

 81.4 



July. 

 84.8 



Aug. 

 84.8 



Sept. 

 85.5 



Oct. 



- 



Nov. 



Dec. 



■ 

 Annual 

 average. 



i 

 77.6 74.2 



71.8 



70.7 



76.7 



82.7 



82.0 



80.7 



79.4 



In most parts of the Archipelago the discomfort one would expect from the 

 continued high temperature and humidity is greatly mitigated by the very general 

 presence of refreshing breezes, particularly at midday and in the afternoon and 

 early evening. The velocity and frequency of the wind in the vicinity of Manila 

 is greatest during the season when the temperature elevation is the greatest 

 ^ March to September). The average daily velocity of the wind for Manila is 

 217.8 kilometers, the monthly aA'erages varying from 149.3 in December to 291.0 

 in September. 



ACTINIC POWEB OF THE STJNLIGHT. 



Of late years the chemical activity of the sunlight has become a factor 

 which, in the opinion of many, should be considered in discussing cli- 

 mate and its influences. Freer, (1) Gibbs,(i4) and Bacon, (15) at the 

 Bureau of Science in Manila, have found that the tropical sunshine 

 produces chemical changes which take place either more slowly or not 

 at all in temperate climates. It has also been shown by Freer that there 

 are in the Philippines "actinic" and "nonactinic days," the chemical 

 action of the sunlight during the latter being much less powerful, even 

 though the sky may seem as clear as on an actinic day. The causes of 

 these differences have not been determined. The investigations at the 

 Bureau of Science have shown that the spectrum of the sun's rays extends 

 into the ultra-violet little if any farther in Manila than in temperate 

 regions. (4) 



That concentrated ultra-violet rays have a harmful influence on 

 bacteria, as well as on some higher forms of life such as protozoa, has 

 been clearly proven by many observations made by ourselves (18) and 

 by others. (19) Some writers, notably Woodruff, (2) (3) have considered 

 that such rays were very injurious to white men, more especially to 



