346 
ON THE STEUCTUEE AND MOTION OE GLAOEES. 
tion, without which it may be doubted whether the existence of a glacier would be at 
all possible, opens, in itself, a new field of investigation. This and other questions, intro- 
duced in the foregoing pages, must however be discussed with strict reference to the 
phenomena as Nature presents them. Much might be said even now upon these subjects, 
but the known liability of the human mind to error when speculation is substituted for 
observation, renders it safer to wait for more exact knowledge, than to hazard opinions 
which an imperfect acquaintance with the facts must necessarily render to some extent 
uncertain. 
Royal Institution^ 
January 1857. 
