2 Fowler, CJiemical Action of Tropical Sunlight. 



This method is, however, not so easily or rapidly 

 carried out, and consequently not so well suited for 

 determinations away from a laboratory, as that used by 

 Dr. Bailey and his colleagues several years ago in Man- 

 chester. The occasion, indeed, at once suggested itself as 

 an interesting opportunity for comparing the chemical 

 intensity of sunlight in Calcutta and elsewhere with the 

 records obtained by Dr. Bailey.* 



The method used by Dr. Bailey is founded upon a 

 reaction originally described by Dr. Albert R. Leeds, of 

 Philadelphia, and independently by Dr. Angus Smith,-|- 

 viz., the liberation of iodine from an acid solution of 

 potassium iodide in presence of air and light according 

 to the following equation : — 



Dr. Angus Smith published a number of preliminary 

 observations as to the effect of temperature, strength 

 of solution, &c., upon this reaction. f He also gave results 

 of the measurement of actinic sunshine in Manchester for 

 a year, and a comparison of the transparency of the 

 Manchester atmosphere in town, suburb, and country.;]; 



The method, as described by Dr. Angus Smith, was 

 modified slightly by Dr. Bailey, with a view to its being 

 used by a number of observers under defined and 

 comparable conditions. 



Dr. Bailey very kindly forwarded to Calcutta the 

 details of the method he used, and a number of interesting 

 comparative results were obtained. Other observations 

 were also made, which, although necessarily of a frag- 



• " The atmosphere of Manchester," G. H. Bailey in "Studies from 

 the Physical and Chemical Laboratories of the Owens College," vol. i, p.25l, 

 1893- 



t Proc. Roy. Soc, No. 203, 1880, p. 355. i6th Ann. Kept, of the Chief 

 Inspector of Alkali Works, 1879, p. 15. 



X ijth Ann. Kept, of the Chiff Inspector of Alkali Works, 1880, p. 16. 



