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- 
^r mometer is immersed, is placed a Bunsen's lamp. The water 
'.. y 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 lamp, there would be no steam, and if there 
'vere 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. This 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 
