THE STUDY OF TROPICAL SUNLIGHT. 9 



In order to compare a climate at higher altitude and but 

 little north of Manila with that of the latter city itself, a series 

 of observations was made at Baguio (Table VIII) (altitude 

 1,432 meters). The temperatures of the nights and in the shade 

 at Baguio are so low that it is an ideal resort for recuperation 

 from the lowland climate, yet the photocatalytic action is much 

 the same, however, with this difference: The maximum at Ba- 

 guio is higher than in the lowlands (20.6 as against 17.8), 

 being in this respect like Honolulu (20.7). The average is 14.2, 

 or 1.75 more than in Manila and 1.09 less than Kuala Lumpur 

 and 0.39 more than Honolulu. The ascent of 1,432 meters has 

 produced the same effect on the photocatalysis as a transfer to 

 Honolulu. The black-bulb readings are practically the same. 

 At Baguio, therefore, as we would expect, we encounter a climate 

 in which the rays undergoing investigation are somewhat more 

 intense than in the lowland. The average temperature in the 

 sun during the observations was 7° to 8° lower than in Manila. 



Manila and Baguio, at present, are the only places where the 

 black-bulb thermometer readings are available simultaneously 

 with the photocatalytic measurements, and a study of individual 

 days demonstrates that the two figures, namely, black-bulb read- 

 ings and percentage of oxalic acid decomposed are not by any 

 means functions of each other; indeed, within reasonable limits 

 they seem to be independent. Of course, it is understood that 

 a certain relationship exists, because, naturally on clear, bright 

 days both black-bulb and photocatalytic readings will be high, 

 and both the reverse on cloudy ones. As an example of these 

 variations, I can cite a few figures taken from daily observations : 



Comparison between photocatalytic and black-bulb readings in Manila. 



From 9 to 12 a. m. 



Weather. 



Photo- 

 catalysis. 



Black 

 bulb 

 (mean of 

 3 observa- 

 tions). 



1910. 

 April 28 



Clear 



16.4 

 17.7 

 13.4 

 16.4 

 14.7 

 16.6 



°C. 

 52.0 

 52.5 

 54.0 

 52.0 

 54.5 

 56. .3 



May 7 



do - 



May 16 





May 18 



Clear 



June 9 



do-.- 



July 5 



Slightly cloudy 











Comparisons of this kind can be extended almost indefinitely, 

 but those given suffice to show that, in the same place and on 

 apparently equally clear days, the relative proportions of the 



