INVESTIGATION OF TEMPERATURE CHANGES. 221 



causes than mere orographic ones have been active in diminishing the 

 amount of precipitation on the earth. It will also be recognized as a fact 

 that a diminiition in the sun's heat would have a similar effect, and we shall 

 now endeavor to show that, aside from the evidence afforded bj the proved de- 

 crease of rain-fall, there are satisfactory reasons for believing that the earth's 

 surface, on the whole, is decidedly cooler than it has formerly been, and that 

 this refrigeration is not a temporary phenomenon, but something which has 

 been going on through all the geological ages. If this be true, it follows, as 

 a matter of coiu'se, that the so-called " Glacial epoch " was not an excep- 

 tional period of cold, which has passed away, and been followed by a return 

 of a previous warmer condition, as is generally affirmed by geologists to 

 have been the case. If, then, a large body of facts can be brought forward 

 indicating that the mean temperature of the earth is becoming lower, it 

 will have to be explained how it could have happened that, at a former 

 time, there were extensive accumulations of snow or ice over certain regions 

 now either nearly or quite destitute of these evidences of a colder climate, 

 — such as glacial phenomena are usually considered to be, — and the occur- 

 rence of which has led to the designation of a certain time in the earth's 

 history as the " Glacial epoch." 



To avoid complication, and to render the discussion more clear, the consid- 

 eration of the Glacial epoch will be reserved for another and special chapter, 

 in which the more prominent and important of the theories of climatic 

 change brought forward by investigators in this line of inquiry will be 

 mentioned, and examined, so far as may appear desirable. The reason for 

 this course will, it is believed, become apparent on reading the chapter 

 in question. 



We have it as our task then, in the present section, to show that there is 

 strong, and it may even be said abundant evidence of a diminution of the 

 solar radiation during the geological ages. Moreover, it will appear on 

 examination that there is a considerable body of facts, aside from those con- 

 nected with desiccation, which justify us in concluding that it is highly 

 probable that this diminution of temperature has been continued into and 

 through the historical period, and has been sufficient in amount during that 

 time to bring about distinctly marked changes of climate, attended by such 

 results as, in certain regions, to be of vital importance to the welfare of the 

 inhabitants. And we may begin the discussion by entering on the last- 

 mentioned inquiry, namely, whether there is any proof of a diminution of 



