ACTION OF THE TROPICAL SUN. 105 



the temperature which, corresponds to the thermic effect of the sun by 

 adding half the number of degrees difference between the register of 

 the black-bulb thermometer in the sun and the shade thermometer to 

 the shade temperature. Applying this calculation to the conditions in 

 the direct sunlight at Manila or other tropical place, for instance, 

 Colombo, we find that this temperature is considerably above the one 

 normal for the body. 



The pyrheliometer devised by Angstrom ^^ alone seems capable of 

 measuring exactly the caloric value of the radiation of the sun. This 

 instrument has been adopted by an international meteorologic conference 

 ia Innsbruck. Measurements with it have been made in other parts of 

 the world, but as yet no work has been done with it in the Tropics. 

 The Eev. Jose Algue, S. J., Director of the Weather Bureau in Manila, 

 has begim such investigations in connection with our experiments. How- 

 ever, an important part of his apparatus was broken, so that after repairs 

 on it had been completed here, we could obtain only relative values for 

 the different days. A new apparatus has been ordered and the figures 

 after its arrival will be recalculated into absolute values.^* 



Therefore, we will shortly be in a position to furnish exact values for 

 Manila and other places in the Philippines obtained by the pyrheliometer. 

 It seems urgent that comparative studies in other parts of the world, 

 especially tropical and subtropical regions, be made with the standard 

 instrument of Angstrom. P. Schmidt estimates the heat effect of the 

 tropical sun as being equal to 2 gram calories per square centimeter per 

 minute. 



I have found in the literature only a few observations concerning the 

 action of the tropical sun on animals. 



Seaghosi " exposed rabbits to the sun in Sicily. Their temperatures rose 

 markedly, and upon continuing the experiment for a sufficient length of time, the 

 animals died. Eecovery took place if the direct insolation was stopped in sufficient 

 time. Castellani and Chalmers " report some experiments which they performed 

 in Colombo. They exposed rabbits with their heads shaved to the noon sun. The 

 animals died in about sixty-seven minutes with all the symptoms and post-mortem 

 appearances of simstroke. Another rabbit, similarly treated, but protected by a 

 red glass, lived. These authors concluded that sunlight can bring about " ( 1 ) 

 sudden death, (2) congestion of the meninges of the brain. The ultra-violet 

 rays seemed to have no effect and it would appear as if the active rays were in 

 the visible violet." Of course the red glass also absorbed a very large proportion 

 of the heat rays. 



"Astrophys. Journ. (1899), 9, 332. 



" My thanks are due to the Rev. Jos6 Algue and to the Eev. Juan Cornelias 

 for the valuable assistance they have rendered, not only by the loan of apparatus 

 and by conducting measurements, but also for advice on meteorologic subjects. 



"Castellani and Chalmers, Manual of Tropical Medicine, London (1910), 86. 



» Ibid. 



