262. TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE _ [VOL. XI 
there is a direction of slowest solubility or greatest resistance. The 
crack beaks are then merely extensions of the longest side of the pit in 
the line of least resistance. 
(c) The normal beaks. 
The processes which result in the formation of normal beaks are, 
like those leading to beaks of the other types, so obscure that any 
attempt at discovering them is beset with many difficulties, but some of 
the facts observed in the foregoing experiments seem to suggest an 
explanation. The fundamental fact should first be noted that the beaks 
always spring from the deepest part of the pit. Many times pits were 
observed which had this deepest part developed in such a way as to 
warrant the conclusion that beaks were just beginning to grow. In 
some cases one of the side walls was seen to be steep, vertical or even 
overhanging. In others, the deepest part, at the base at such a steep 
side had become enlarged so as to form a knob-like projection. The 
forces acting upon a particle of the solvent in such a narrow corner, 
are indicated in the diagram. Of the four figure faces here indicated 
oO d 
b re 
in the diagram, the longest, b, is the most slowly attacked and therefore 
has the least attraction for the particles of the solvent, while the 
smaller, a, c, and d, are those of most rapid solution and therefore 
of greatest attraction. In consequence each particle of the solvent 
is under the influence of forces which draw it toward the faces 
illustrated, and will move in the resultant direction e. The most 
° ins me | 
saa Eee 
Lise 
b a . 
e 
rapid solution, then, will take place at the point where the line of motion 
strikes a face of the pit. The result of such action will naturally be to 
accentuate the depth of the deepest part. 
