note the intensity of the force acting tangentially on the sides on 

 which X acts normally. It is proved that/ will also be the inten- 

 sity of the tangential force on the other two sides. Then, if 9 be 

 the angle which the line of maximum tension through the proposed 

 element makes with the axis of the glacier, it is proved that 



tan 2 9 



_ 2/ 



X-Y' 



where X and Y are tensions. If either be a pressure, it must be 

 made negative. 



If the maximum tension become greater than the cohesion of the 

 ice, a fissure will be formed in a direction perpendicular to that of 

 the tension at each point, or at least approximately so. Conse- 

 quently, the line whose direction is defined by the angle 9, will be a 

 normal to the curve of fracture. Now, taking the case in which 

 the glacial valley contracts in descending (which is the more frequent 

 case), Y is doubtless most frequently a pressure, in which case 



also / will be greatest at the sides (where the velocities of particles 

 in a transverse line vary most rapidly), and will vanish at the centre. 

 Hence 9 will vanish at the centre of the glacier, and will increase 

 towards the sides, since the change in the value of the denominator 

 cannot be great. Consequently, if a fissure were continued across 

 the glacier it would form a curve, meeting the axis of the glacier at 

 right angles ; and its convexity will be turned towards the upper ex- 

 tremity of the glacier, for the line defined by the angle 9, or the 

 normal to the curve, meets the axis of the glacier when produced 

 towards its lower extremity. This is the well-known character of 

 transverse fissures, which the author conceives to be thus completely 

 accounted for. In the previous memoir above referred to, this cu- 

 rious character had been very imperfectly explained by referring it 

 to the action of the longitudinal tension (X) alone. 



In conclusion the author has replied to the objections against the 

 sliding theory urged by Prof. Forbes and others. 



February 5, 1844. 



On the Fundamental Antithesis of Philosophy. By W. Whewell, 

 D.D. 



The fundamental antithesis here spoken of, is that which is vari- 

 ously expressed by the opposition of thoughts and things, theory and 

 fact, ideas and senses, necessary and experimental truth ; also by 

 the opposition of reflection and sensation, subject and object. It is 

 remarked that we can have no knowledge without the union, no 

 philosophy without the separation of these two elements. This fun- 

 damental antithesis of philosophy is an antithesis of inseparable ele- 



