A STUDY OF THE EFFECT OF TROPICAL SUNLIGHT UPON MEN, 



MONKEYS, AND RABBITS AND A DISCUSSION OF THE 



PROPER CLOTHING FOR THE TROPICAL CLIMATE.' 



By H. D. GiBBS/ 



{From the Laboratory of Organic Cheviiatry, Bureau of Science, and the 

 Department of Chemistry, University of the Philip-pines, Manila, P. I.) 



INTRODUCTION. 



The literature which treats of tropical sunlight as distinct 

 from sunlight in other parts of the world is very voluminous, 

 and tends throughout to show that the sunlight shining upon 

 tropical regions is different from that encountered in other 

 latitudes. It is true that the sunlight which reaches the surface 

 of the earth is different not only in various localities, but also 

 in the same localities on different days and at different times 

 of the same day. The character of the light and its intensity 

 are subject to variations, and these two factors are regulated 

 by the media through which the light passes; namely, the gases 

 of the atmosphere and suspended matter. Any absorption in 

 the space beyond the atmosphere of the earth does not, of course, 

 enter into this consideration. 



The light which reaches the surface of the earth is composed 

 of the ultra-violet rays about as far as 291 fi/x,'- the rays of 

 the visible spectrum, and the infra-red. Every region of this 

 spectrum may be altered in the passage of the rays through the 

 atmosphere due to absorption, reflection, molecular scattering, 

 and refraction; and thus, it is seen that at any one place the 

 sunlight which reaches the surface of the earth is influenced 



' This paper was submitted for publication in November, 1911. 



' Associate professor of chemistry. University of the Philippines 



" I have taken a large number of photographs of the sun's spectrun at 



sea level and at an elevation of 1,512 meters in the Philippines, and the 



results will be ready for publication shortly. 



91 



