56 THE WONDERFUL CENTURY. CHAP. vn. 



curved, and the curvature may be increased to any de- 

 sired extent if force is applied for a sufficient time. 

 Models of glaciers in cobbler's wax, which is brittle at 

 ordinary temperatures, exhibit all the phenomena of true 

 glacier-motion, and serve to demonstrate the upward 

 motions above referred to, which have been so often de- 

 nied. Most metals exhibit similar phenomena under 

 suitable conditions, and lead can be made actually to flow 

 out of a hole under pressure. 



One of the most characteristic properties of gases and 

 liquids is that of readily mixing together when placed 

 in contact. But it has recently been shown that solids 

 also mix, though very much more slowly. If a cube of 

 lead is placed upon one of gold, the surfaces of contact 

 being very smooth and true, and be left without any 

 pressure but their own weight, and at ordinary tempera- 

 tures, for about a month, a minute quantity of gold will 

 be found to have permeated through the lead, and can be 

 detected in any part of it. Metals may thus be said to 

 flow into each other. 



In order to produce chemical changes in bodies, it is 

 usually necessary that one at least be a liquid or be in a 

 state of solution, and the combinations that occur lead to 

 the production of bodies having quite different proper- 

 ties from either of their components. Similar results 

 occur when metals are mixed together, forming alloys. 

 Thus a mixture in certain proportions of lead, tin, bis- 

 muth, and cadmium produces an alloy which melts in 

 boiling water, while the component metals only melt at 

 double that temperature or more. Again, the strength 

 of gold is doubled by the addition of one five-hundredth 

 part of the rare metal zirconium, indicating that the 



