Manchester Me7noirs, Vol. lii. {igo'B,), No. \4. 15 



geographical position in reference to the equator. The 

 author is not aware how far this is borne out by experience 

 in other tropical countries. It is not quite easy to see, if 

 the sunstroke effect is neither a heat effect nor a photo- 

 chemical effect, why it should depend on the verticality of 

 the rays. The question may perhaps be left to the 

 physicists and medical men to discuss. 



There would appear to be some relation between 

 photo-chemical activity and snnburii. A very short 

 inadvertent exposure of a lady's short sleeved arm on the 

 gunwale of the tender, while changing steamers at Aden, 

 caused considerable reddening and final peeling of the 

 skin, while the often rather serious effects of sunburn in 

 the Alps are familiar. In this latter case temperature can 

 hardly be a factor. On the other hand, the author has 

 spent a good many days working out of shelter in full sun 

 in the neighbourhood of Calcutta, without being as 

 sunburnt as after a few days by the sea in this country. 

 As in the case of sunstroke, some other factors than photo- 

 chemical activity and temperature would appear to be 

 concerned with the phenomenon of sunburn. 



TJic Absorption of Photo-cJicniical Rays. 



The absorbing effect of iodine solutions has already 

 been referred to. Dr. Bailey remarks {Joe. cit. p. 253) 

 that the photo-chemical rays are almost completely 

 absorbed by a solution of bichromate of potash and by 

 chlorophyll. 



A few experiments were made on the absorbing effect 

 of various solutions, by exposing the standard mixture 

 to light in a narrow test-tube placed within a larger one, 

 the absorbing solution being contained in the annular 

 space between the two test-tubes. The arrangement 



