Mr. Hopkins's Remarks on Prof. Forbes's Reply. 595 



these phaenomena be appealed to as experimental tests of the 

 truth of either ? I refer your readers to the whole passage 

 in my Third Letter (Phil. Mag. for March, p. 248)*; I re- 

 assert the truth of what is there stated. 



So much for my misstatements. The first is no statement 

 at all; if the second be a misstatement, it is due to the Pro- 

 fessor himself; and the third I reassert as a correct statement. 

 The general problem of glacial motion as considered by 

 Prof. Forbes and myself, naturally resolves itself into two 

 parts — the cause of motion, and the internal tensions, press- 

 ures, &c. which result from it. In considering this latter 

 part of the problem, Prof. Forbes arrived at the conclusion 

 that the direction of maximum tension at any point coincided 

 with that of the loop through that point, whence also he 

 deduced another conclusion, viz. that the same direction also 

 coincided with that in which there is the greatest tendency in 

 one particle to slide past another. On these two conclusions 

 his whole theory of the laminar structure entirely rests ; if 

 they be untenable his theory ceases to exist. How then stands 

 the matter at present ? The first conclusion is given up as 

 an oversight, and the correctness of my investigation on this 

 point is tacitly admitted. The second conclusion is not ex- 

 plicitly surrendered, though not retained with any explicit de- 

 claration in its favour. In fact, if the correctness of my re- 

 sults on the first point be allowed (and they are too obvious to 

 be controverted), I defy any ingenuity to disprove the accu- 

 racy of my conclusions on the second point. We might as 

 well deny the proposition of the lever, while we allow the par- 

 allelogram of forces. No hypothesis as to the properties of 

 matter is made in one part of the investigation which is not 

 involved in the other; so that if Prof. Forbes would be con- 

 sistent with himself, he must either show that I have com- 

 mitted some mathematical blunder, or he must admit a second 

 oversight in his own reasoning as obvious as the first. 



But, says the Professor, my writings on the subject are so 

 voluminous that he cannot undertake to go through them. 

 Now the little pamphlet comprising the four letters on glacial 

 motion which you have done me the honour to publish, and 

 containing the full development of my views on the subject, is 

 now lying before me in juxtaposition with the royal octavo 

 of Prof. Forbes, and when I compare the lean and jejune look 

 of my own volume with the portly and royal bearing of its 

 neighbour, I cannot but think the Professor's taunt of my 

 having written so much either a piece of the most obvious 

 irony, or as one of the most unreasonable charges that con- 

 * See also the Introduction to my first memoir. 

 2 R2 



