THE TROPICAL SUNLIGHT. 13 



those of Hertel on the pigments of natural tissue, have shown that the 

 absorption of the former for ultra violet light differs markedly accord- 

 ing to the nature of the chemical individual employed. 



While Hertel's investigations have no direct bearing, at present, on the 

 subject of tropical sunlight, because concrete and connected experiments 

 in the Tropics are lacking, still the coloration of phenol and aniline, 

 the oxidation of methyl alcohol, the rapid decomposition of oxalic acid 

 in the presence of uranium acetate, and the intense ionization of the air 

 in Manila, are possibly referable to a larger proportion of ultra-violet 

 light in the sun's spectrum at this latitude ; and therefore, if this be so, 

 it will also be true that living tissues will be affected abnormally, or, in 

 other words, we should expect the effects of tropical sunlight upon micro- 

 organisms and those of a higher order, and the consequent endeavor by 

 pigmentation or other means of these organisms to protect themselves, 

 to be similar to those observed by Hertel for the ultra-violet in his spec- 

 troscopic investigations. Of course, we must not lose sight of the fact 

 that the tropical sunlight probably displays a greater intensity of all 

 rays, and that this effect would be cumulative. 



Ewart 18 calls attention to the fact that plants in the sunlight of the Tropics 

 seek to protect themselves by the production of a red color ( ery throphyll ) the 

 absorption spectrum of which has a band in the violet. In a journey to Java 

 he observed that the red color of the leaves was more common and marked in 

 the low, tropical valleys than higher up on the mountains. In the cloud-covered 

 belt it was entirely absent, but above the latter it again appeared. 



However, it has not been proved that the tropical sunlight really does 

 contain a greater proportion of ultra-violet light than that of northern 

 climates. So far, we can only come to the conclusion that it has a greater 

 intensity, as the experimental work which I have given has shown, and 

 that a certain proportion of rays lying in the ultra-violet is present. 

 Greater intensity, although with but a small area in the latter portion 

 of the spectrum, would bring about results similar to those which would 

 be observed if the light extended to 280 /*//. beyond. 



THE SPECTRUM OF THE SUN IN MANILA DURING FEBRUARY, 1910. 



We have endeavored to solve this problem in Manila by the construc- 

 tion of an instrument from such means as are at hand. Funds have 

 heretofore been lacking to have made by the best mechanics of America 

 or Europe a spectro-photographic apparatus entirely adapted to the 

 needs of the investigation. 



Our spectroscope consists of a Rowland grating, a heliostat, both very kindly 

 loaned to us by the Philippine Weather Bureau, 1 " and a quartz lens and slit taken 



a Journ. Linn. Soc. (Bot.) (1895), 31, 3G4; Ann. Bot. (1897), 11, 440. 



10 1 wish at this place to express my sincere thanks to the Reverend Father Josfi 

 Algug, Director of the Weather Bureau, at Manila, for his loan of apparatus 

 and his most kindly cooperation in all that we have asked of him. 



