14 Fowler, Chemical Action of Tropical Sunlight. 



On the following day (May 9th, 1906) a further experi- 

 ment was made, the second bottle in this case being 

 suspended one inch above the surface of the water in a 

 large open tub coated inside with white enamel, the 

 control being on a white plate as usual, and both in full 

 sun. The period of observation was from 11-30 a.m. to 

 12 noon. The position of the steamer was about lat. 

 I3"59) long. 48'37, some two miles from the Arabian 

 coast. The control again gave the higher result, viz., 

 34 mgms. iodine per 100 c.c. per hour as against 22 mgms. 

 in the case of the bottle suspended over the water. 



It may be concluded, therefore, that the chemical rays 

 are not reflected from the surface of the water to the same 

 extent as from such a surface as is presented by white 

 porcelain, and to no greater extent than from the ordinary 

 white planking of the deck. 



From the results which are here recorded, it would 

 thus appear that no relation exists between the photo- 

 chemical and the sunstroke effect of sunlight. This is 

 confirmed by the fact, that pith helmets are considered 

 equally necessary in India on dull or bright days. The 

 author was informed that many sunstrokes occur on dull 

 days in Calcutta through carelessness in uncovering the 

 head. 



On the other hand the effect can hardly be one of 

 temperature, as " topis " have to be worn both in the hot 

 and cold weather in India, and also, as has been stated, in 

 the hills. Moreover they are not worn in Melbourne, 

 where the temperature may often be as high as in India. 

 It is, of course, possible that rays other than either the 

 actinic or the ultra red rays may have to do with the 

 phenomenon of sunstroke. 



It has further been supposed that the effect depends 

 on the verticality of the sun's rays, and consequently, on 



