CONDITIONS AFFECTING PRECIPITATION. 203 



sun as the land masses can be. With the great expanse of Africa adjacent 

 it is not possible that similar effects should be produced in the countries to 

 the west of India. Wliat little does result in that direction is not enough to 

 remove the general character of dryness and consequent desolation impressed 

 on the whole region by the combination of unfavorable circumstances. 



From what has been said in the preceding pages it is thought that the 

 reader will have been fully convinced of the truth of the statement that 

 the form, size, and position of the land masses change the whole character of 

 the distribution of the precipitation from what it would normally be were the 

 earth entirely covered by water ; the eflect of this being that certain regions 

 are entirely deprived of moisture, while upon others the rain-fall is enormous 

 in amount. It has also been shown on what conditions the total amount of 

 precipitation on the earth depends : that if this amount were considerably 

 increased a proportionate irregularity in its distribution would be main- 

 tained, there seems to be no reason to doubt. 



The amount and distribution of the fall of I'ain and snow in the polar re- 

 gions is a branch of the present inquiry in regard to which our data are far 

 from being satisfactory in kind or amount. The published rain-charts afford 

 but little light on this subject. That, as a general rule, precipitation is much 

 smaller in high northern latitudes than neai'er the equator has already' been 

 stated. Professor Loomis says: " Be^^ond the parallel of G0° N. latitude, at 

 a little distance from the ocean, the mean annual rain-fall seldom much 

 exceeds ten inches ; and there are apparently regions of great extent in 

 Asia and North America where the annual rain-fall is less than ten inches."* 

 But that the precipitation is very irregularly distributed in the Arctic lands 

 and seas is probable ; and that it is very large over a certain area is hardly 

 to be denied. In retj-ard to the Antarctic rejjion we know even less than we 

 do of the opposite pole. This ignorance of the meteorological conditions of 

 the polar areas is all the more to be regretted, since the conditions in those 

 parts of the earth are continually being appealed to by glacial geologists 

 as illustrations of what took place in lower latitudes during the " Glacial 

 epoch." It will be best, therefore, to reserve what we have to say on the 

 subject of the precipitation in the north and south polar regions until the 

 next chapter, when a concise statement will be given of all that is definitely 

 known of the meteorological conditions prevailing in the extreme northern 

 and southern latitudes. 



* Contributions to Meteorology. Sixteenth Paper, Am. Jour. Sci. (3) XXIII. p. 22. 



