EFFECT OF TROPICAL SUNLIGHT ON THE ATMOSPHERE. 271 



Wilson 8 showed that with intense ultra-violet light, clouds are produced in 

 air, or in oxygen, with a minimum amount of expansion, and he assumes that 

 these clouds are primarily deposited on nuclei connected with the formation of 

 hydrogen peroxide. This does not take place when hydrogen is the gas used, 

 and Thomson ° has shown that, whereas air bubbled through water is strongly 

 charged and contains a large proportion of negative ions, with hydrogen gas the 

 ionization is exceedingly small. 



These experiments seem to me to indicate that the formation of 

 hydrogen peroxide is an essential intermediate step in these reactions. 

 When pure water, or a salt solution is exposed to direct sunlight in 

 Manila, hydrogen peroxide is formed very rapidly, strong tests being 

 obtained after a few hours. H. D. Gibbs, 10 of this Bureau, who examined 

 the solutions in a great number of reagent bottles exposed in the labor- 

 atory for some months to diffuse light, found in practically every case 

 considerable quantities of hydrogen peroxide. It is evident that in the 

 Tropics, at least in island regions, with the great quantity of vegetable 

 growth, the vigorous transpiration of plants, and the large amounts of 

 .water continually present at the surface of the earth and in the air, 

 all the conditions are present when the sun is shining which are neces- 

 sary to charge the area of water surfaces, to form peroxide of hydrogen, 

 and in. general to increase the proportion of ions in the air according to 

 the processes which have been outlined above. Whether there is a true 

 ionization of the air by tropical sunlight, apart from such a secondary 

 ionization, must be determined by further studies. Considerable evi- 

 dence is accumulating to show that the tropical sunlight contains more 

 intense ultra-violet light than that in temperate zones. Thus, I have 

 shown in another paper 1X that the decomposition of oxalic acid or of 

 oxalic acid catalyzed by uranium salts, is very much more rapid in the 

 Philippines than in temperate zones, and Gibbs 12 has shown that the 

 coloration of phenol and of aniline takes place much more rapidly in 

 the Tropics than in more northern zones. 



One of the most striking effects produced by ions is the influence they 

 exert on the condensation of clouds. I have often noted, in watching a 

 steam jet in the open air in Manila, the remarkable way in which, as the 

 sunlight strikes it, it becomes dense and beautifully colored, due to the 

 interference and diffraction of the light by the small drops of water, 

 while as soon as the sun goes behind a cloud, the jet becomes very 

 thin, and the colors, of course, disappear. Other conditions being equal, 

 on a cloudy day the mountains near Manila can be seen much more 



8 Loc. rit. 



9 Loo. cit. 



10 Unpublished research. 



11 This Journal, Sec. A (1910), 5, 



"This Journal, Sec. A (1910), 3, 361; Ibid. (1909), 4, 133; Ibid. (1910), 

 5, 9. 



