Staler.] 178 [October 6, 



any country would be necessarily attended by a perceptible variation 

 in its rainfall, while by a change of five hundred feet the effects 

 might be of great importance in the distribution of animals and 

 .plants. The change of the height of other regions may have as 

 important an influence as the elevation or depression of the given 

 district. In fact, the interaction of these causes leads to very com- 

 plicated phenomena, which it is far beyond my purpose to consider. 

 It is evident that they may be grouped together under the general 

 term of the influence of height. This is probably by far the greatest 

 determining influence of a local kind. 



Along with this cause comes the position of areas of evaporation; 

 the height and conditions of a country being unaltered in every re- 

 gard, a variation in the evaporation region which supplies it may have 

 a great effect upon its rainfall. If a considerable part of the evapo- 

 ration areas supplying North America became dry land, the effect 

 must be great without any cooperating action occurring on the conti- 

 nent itself. 



Change in the direction or force of ocean currents would also 

 have great effects. When the Japan current entered the Arctic 

 Ocean, giving that region the warmth it had when its vegetation 

 resembled that existing in the Mississippi Valley at the present 

 time, there probably was a material increase of the rainfall there, 

 and probably a diminution of the deposition in the tropical region, 

 caused by the considerable lowering of heat in that region, while a 

 large part of its temperature was being dissipated in the Arctic Ocean. 

 These considerations seem to confirm us in our belief in the very 

 great variability of the conditions which affect the distribution of 

 the rainfall, assuming it to remain constant over the world at large. 

 Enough has been written concerning the influence of forests, etc., to 

 make it unnecessary to advert to these influences in this paper. s 



Turning now to the conditions which may affect the total amount 

 of water lifted from the earth's surface during the year, we come 

 to a class of questions which have been very little considered by 

 meteorologists, and possibly with good reasons, since the main aim 

 of the real advancers of that science is to keep out of the field of 

 pure conjecture. It will, I trust, be evident, however, that some- 

 thing can be gained from a glance at this question without becoming 

 too speculative in our considerations. 



The most material influence which can come from the elevations 



