164 FRAGMENTS OF SCIENCE. 



motive powers invoked in scientific investigation. True he" 

 lacked mechanical precision, but he abounded in that force 

 and freshness of the scientific imagination which in some 

 sciences, and probably in some stages of all sciences, are 

 essential to the creator of knowledge. To Agassiz was 

 given, not the art of the refiner, but the instinct of the dis- 

 coverer, and the strength of the delver who brings ore from 

 the recesses of the mine. That ore may contain its share 

 of dross, but it also contains the precious metal which 

 gives employment to the refiner, and without which his 

 occupation would depart. 



Let us dwell for a moment upon this subject of ancient 

 glaciers. Under a flask containing water, in which a ther- 

 mometer is immersed, is placed a Bunseu's lamp. The water 

 is heated, reaches a temperature of 212 degrees, and then be- 

 gins to boil. The rise of the thermometer then ceases, al- 

 though heat continues to be poured by the lamp into the 

 water. What becomes of that heat? We know that it is con- 

 sumed in the molecular work of vaporization. In the exper- 

 iment here arranged, the steam passes from the flask through 

 a tube into a second vessel kept at a low temperature. Here 

 it is condensed, and indeed congealed to ice, the second 

 vessel being plunged in a mixture cold enough to freeze the 

 water. As a result of the process we obtain a mass of ice. 

 That ice has an origin very antithetical to its own char- 

 acter. Though cold, it is the child of heat. If we re- 

 moved the 2amp, there would be no steam, and if there 

 ^ere no steam there would be no ice. The mere cold of the 

 mixture surrounding the second vessel would not produce 

 ice. The cold must have the proper material to work upon; 

 and this material aqueous vapor is, as we here see, the 

 direct product of heat. 



It is now, I suppose, fifteen or sixteen years since I 

 found myself conversing with an illustrious philosopher 

 regarding that glacial epoch which the researches of 

 Agassiz and others had revealed. Tins profoundly thought- 

 ful man maintained the fixed opinion that, at a certain 

 stage in the history of the solar system, the sun's radiation 

 had suffered diminution, the glacial epoch being a conse- 

 quence of this solar chill. The celebrated French math- 

 ematician Poisson had another theory. Astronomers 

 have shown that the solar system moves through space, 

 and "the temperature of space" is a familiar expression 



