MR.. GORDON ON THE GLACIER-LIKE MOTION OF PITCH. 269 



APPENDIX, No. IV. 



ACCOUNT OF AN EXPERIMENT ON STOCKHOLM PITCH, 

 CONFIRMING THE VISCOUS THEORY OF GLACIERS. 

 In a Letter from Professor GORDON of Glasgow to Professor J. 

 D. FORBES of Edinburgh. Communicated by Professor J. D. 

 Forbes in a Letter to Richard Taylor, Esq.* 



To RICHARD TAYLOR, Esq. 



My dear Sir The inclosed communication from Mr. Gordon, 

 Professor of Civil Engineering in the University of Glasgow, which 

 he has allowed me to transmit to you for publication, will, I believe, 

 be found interesting to your readers. The fact that pitch is suscep- 

 tible of slow fluid motion, whilst it retains the character (in hand 

 specimens) of a brittle solid, with a conchoidal fracture and glassy 

 lustre, may assist in resolving the doubts of some impartial persons 

 who have thought these characters in ice to be incompatible with such 

 a motion as my theory of glaciers requires, whilst the structural bands 

 having the frontal dip complete the analogy. I remain, etc. 



JAMES D. FORBES. 



EDINBURGH, February 6, 1845. 



To PROFESSOR FORBES. 



" When you requested me to give you a memorandum of what ap- 

 peared to me to be the very glacier-like motion and appearance of 

 Stockholm pitch flowing from a barrel, I considered my observation to 

 have been too casual to be worth writing, and having foreseen that I 

 could arrange an experiment at Gateshead in the beginning of the 

 year, I delayed giving you the memorandum you wished. I had hoped 

 to have been able to inspect and report on my experiment about this 

 time, but I cannot go to Gateshead for some time to come, nor have I 

 had any report of the progress of my pitch glacier since the 6th of 

 January, when I was informed it had not moved since the day after 

 I left it on the 28th of December. Your note of yesterday induces 

 me to offer you the following still perfectly vivid impressions of the 

 analogy between ice and Stockholm pitch. 



* [Philosophical Magazine, March 1 845. This paper ought to have been referred 

 to at page 92.] 



