2 8o THE POPULAR SCIENCE MONTHLY. 



always perfect. Some point is perhaps taken for granted, some pe- 

 culiar circumstance is overlooked. Or else our exjilanation agrees 

 with the facts not perfectly, hut merely in an approximate manner, 

 leaving a something still to be accounted for. Now, these residual 

 phenomena, these very anomalies, may become the guides to new and 

 important revelations. 



In the course of my research anomalies have sprung up in every 

 direction. I have felt like a traveler, navigating some mighty river 

 in an unexplored continent. I have seen to the right and the left 

 other channels opening out, all claiming investigation, and promising 

 rich rewards of discovery for the explorer who shall trace them to 

 their source. Time has not allowed me to undertake the whole of a 

 task so vast and so manifold. I have felt compelled to follow out, as 

 far as lay in my power, my original idea, passing over reluctantly the 

 collateral questions springing up on either hand. To these I must 

 now invite the attention of my fellow-workers in science. There is 

 ample room for many inquirers. 



Nor must we forget that the more rigidly we scrutinize our re- 

 ceived theories, our routine explanations and interpretations of Nature, 

 and the more frankly we admit their shortcomings, the greater will he 

 our ultimate reward. In the practical world fortunes have been real- 

 ized from the careful examination of what has been ignorantly thrown 

 aside as refuse ; no less, in the sphere of science, are reputations to be 

 made by the patient investigation of anomalies. Advance Sheets of 

 Quarterly Journal of Science. 



-- 



THE CAUSES OF THE COLD OF THE ICE PERIOD. 



Br Pbof. J. S. NEWBEEEY, 



OF COLUMBIA COLLEGE. 



A FEW years ago the scientific world was startled by the asser- 

 tion made by Charpentier and Agassiz, who had been study- 

 ing the glacial phenomena of Switzerland that at no very remote 

 period, geologically speaking, the climate of the northern hemisphere 

 had been very much colder than at present ; and that the arctic con- 

 ditions which now prevail in Greenland with perpetual snow-sheets, 

 and glaciers reaching the sea extended as far south as the middle of 

 the present temperate zone. 



At first, seriously questioned by most, strenuously denied by some, 

 this theory was found to be sustained by such abundant and indis- 

 putable evidence the inscriptions left by the glaciers themselves 

 that it was not long before it had secured a general acceptance from 

 geologists. Since then there has been a vast amount of. theorizing 



