ADVANTAGE OF DRY AIR 



23 



The advantage of California over Eastern and Southern fruit 

 regions in the abundance of clear sunshine is shown in the adjacent 

 table. Cloudiness is rated from to 10, three observations daily, 

 and the figures in the table are the averages from these daily 

 observations for a series of years, compiled from the records of the 

 U. S. Weather Bureau. 



RELATION OF ATMOSPHERIC HUMIDITY TO THE 

 GROWTH OF TREES 



There is another important condition of the climate of California 

 which is intimately related to those which have been considered, 

 and which is to be credited with no small influence in the perfection 

 of our fruits, and that is the low percentage of humidity which our 

 atmosphere contains. In California the percentage of humidity is 

 high in the winter and low in the summer; in the East the condi- 

 tion is just reversed. For this reason summer heat is far more 

 oppressive in the East than in California, and for the same reason 

 certain serious fungoid diseases which prevail at the East, though 

 found here in less injurious degree directly on the coast, are wholly 

 unknown in the interior where the air is drier. The dry air also 

 favors the access and action of light and heat, for Tyndall says that 

 a sheet of vapor acts as a screen to the earth, being in a great 

 measure impervious to heat. 



Normal relative humidity at Eastern and California points 



Avg. for 

 Eastern Stations April May June July Aug. Sept. Oct. Nov. 8 mo. 



Jacksonville, Fla 72.3 73.0 77.6 78.6 80.9 82.9 79.8 82.2 78.3 



Philadelphia, Pa 63.4 68.9 69.2 68.6 71.2 75.2 70.7 73.6 70.1 



Rochester, N. Y 67.8 68.6 69.1 67.3 70.7 75.2 75.6 76.2 71.3 



Grand Haven, Mich... 70.9 71.4 73.7 69.0 73.1 75.0 75.7 79.1 73.5 



St. Louis, Mo 63.7 67.8 68.8 66.3 67.3 70.2 65.9 71.1 67.6 



New Orleans, La 76.0 74.2 78.1 78.3 78.8 77.3 74.0 79.4 78.0 



Galveston, Tex 84.6 78.0 79.3 77.4 78.1 77.2 75.6 80.4 78.5 



It is not necessary, then, that there should be clouds to lessen 

 the chemical effects of sun heat in fruit ripening. Not only do 

 clouds intercept sunshine, but water vapor in the air when to the 

 eye the sun is bright as ever can absorb a large quantity of the 

 effective sun rays, and so retard fruit ripening. Hence an appar- 

 ently sunny country which has much invisible water vapor in the 

 air, may prove defective in fruit-ripening qualities. 



