272 BACON. 



clearly than on one of sunshine, and I do not believe I err when I state 

 that all days of bright sunshine in the Philippines show a decidedly 

 hazy atmosphere, as noted by looking at objects at some distance. I 

 believe this fact to be due to the ionization of the air by the sunlight 

 and the consequent condensation of very minute drops of water around 

 the ions so formed. The mountains are most clearly visible from Ma- 

 nila at sunrise and at sunset and on days when clouds protect the lower 

 atmosphere from the ionizing radiations of the sun. 



It is an important meteorologic question whether direct sunlight can 

 produce a cloud in the atmosphere without expansion. Wilson 1:! was 

 not able to obtain a cloud in a closed vessel in sunlight with less than 

 the normal expansion, 1.25. He points out that the conditions in the 

 open air are more favorable to the production of clouds than those in 

 a closed vessel, for in the latter the drops might diffuse to the sides 

 before they had time to grow to a visible size, while in the atmosphere 

 this way of escape would not be open to them. It is an interesting fact 

 that the Philippine Weather Bureau in twenty years of daily observation, 

 has never observed a cloudless day in Manila. In traveling on the sea, 

 where disturbing factors due to land surface, vegetation, etc., are absent, 

 it is always noted that as one enters the Tropics the air becomes more 

 hazy, especially on bright sunshiny days, a fact which I have often ob- 

 served and which has been confirmed by me many times in conversation 

 with sea captains. As to whether this is due to greater ionization of 

 the air by means of light in the Tropics, or simply to the fact of there 

 being more moisture in the air to condense around ionic nuclei, must be 

 determined by future work. I incline to the view that both factors 

 cause this increased haziness. Apart from the experimental work which 

 seems to show a greater intensity of ultra-violet light in the Tropics and 

 apart from the more direct incidence of the sun's rays into the atmos- 

 phere of these regions, resulting in less refraction and consequently in 

 less loss of the shorter waves of light, there are. other theoretical con- 

 siderations which seem to point to a greater intensity of ultra-violet light 

 for this zone. The absorption of light by water in the air is quite 

 marked in the red end of the spectrum and comparatively slight in the 

 ultra-violet. The amount of moisture in the air of the Tropics during 

 a year is greater than in temperate zones ; also the total amount of radia- 

 tion received from the sun in the course of a year is greater in the 

 Tropics than in more northern or southern latitudes. Hence, as the 

 longer rays corresponding to the red end of the spectrum are propor- 

 tionately much more strongly absorbed by the atmosphere in the Tropics, 

 and as the total radiation reaching the earth is also much greater than 

 in temperate zones, both the proportionate and the absolute quantities of 



13 Loc. cit. 



