] 46 Canon Moseley on the Mechanical Impossibility 



former supposes its weight a force sufficient to do so in the solid 

 state ; the latter, to make it sufficient, half melts it. 



If, according to my present argument, the descent of a glacier 

 by its weight only is impossible, neither of these theories is ad- 

 missible. Agreeing with the pressure theory as to the essential 

 solidity of glacier-ice, and with the viscous theory as to the in- 

 sufficiency of the weight of the ice alone to cause it to descend 

 in the solid state in the stream-like way in which it actually 

 does descend, I have ventured to propose a theory which calls 

 in aid of its weight the dilatations and contractions of its mass 

 caused by alternations of temperature. 



To arrive at some knowledge, however imperfect, of the elas- 

 ticity of ice from its deflection under given deflecting forces, I 

 made the following experiments on the 28th of December, 1869, 

 when the temperature of the air was considerably below freezing. 

 I caused planks of ice to be taken from the surface of a pond, 

 and carefully sawn into rods and planed on a carpenter's bench 

 and squared. It was very difficult to do this, because of the 

 extreme brittleness of the ice. The surface nevertheless worked 

 easily under the plane, and was quite dry (in that temperature 

 of the air) and beautifully smooth. My first experiment was 

 with a rod of ice 4 \ inches wide by 1^ inch thick, which I placed 

 horizontally on bearings 3 feet 3 inches apart. When loaded in 

 the middle v/ith a weight of 

 12 lbs. it broke after de- 

 flecting T \ inch. The frac- 

 ture was probably caused 

 by some motion given to 

 the last instalment of the 

 weight in the act of being 

 placed upon it. The surface 

 of fracture was continuous 

 and symmetrical; and hav- 

 ing been repeated under the same geometrical form in all the 

 similar experiments which I made, I append a diagram copied 

 from a tracing of it. 



In a second experiment I placed a rod of ice, lj\ inch broad 

 by ^ inch thick, horizontally upon bearings 3 feet apart — and 

 beside it a rod of wood resting on the same bearings, and ad- 

 justed so as to serve as a straight edge. To this rod of wood a 

 small ivory rule, divided into fiftieths of an inch, was fixed verti- 

 cally to measure the deflections of the rod of ice in the middle. 

 By its own weight alone, which was 11*713 oz., it deflected 

 •04 inch. 



The following Table shows its deflections when loaded in the 

 middle with other weights :— 



