THE PARALLEL ROADS OF GLEN ROT. 
381 
forsaken. The subject of glacier extension was subsequently- 
followed up with distinguished success by Charpentier, Studer* 
and others. Agassiz grappled with it with characteristic vigour, 
extending his evidences far beyond the domain of Switzerland. 
He came to this country in 1840, and found in various places 
indubitable marks of ancient glacier action. England, Scotland,, 
Wales, and Ireland he proved to have once given birth to- 
glaciers. He visited Glen Hoy, surveyed the surroundings 
neighbourhood, and pronounced, as a consequence of his investi- 
gation, the barriers which stopped the glens and produced the 
parallel roads to have been barriers of ice. To Mr. Jamieson* 
above all others, we are indebted for the thorough testing and 
confirmation of this theory. 
And let me here say that Agassiz is only too likely to bo 
misrated and misjudged by those who fail to grasp in their 
totality the motive powers invoked in scientific research. 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 discoverer, 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 thermo- 
meter is immersed, is placed a Bunsen’s lamp. The water is 
heated, reaches a temperature of 212°, and then begins to boil. 
The rise of the thermometer then ceases, although heat con- 
tinues to be poured by the lamp into the water. What becomes 
of that heat ? We know that it is consumed in the molecular 
work of vaporization. In the experiment 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 character. Though cold, it is the child of heat. If 
we removed the Bunsen lamp, there would be no steam, and if 
there were 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 vapour — 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 
