416 Mr. W. Mathews on Canon Moseley's views 



The first has been challenged more than once in the course 

 of the controversy, without eliciting any rejoinder from Canon 

 Moseley, no doubt from the absence of any materials available 

 for the support of the hypothesis. The fact is, that while we 

 have numerous observations of the absolute motion of various 

 points of the surfaces of glaciers, observers do not appear to have 

 been sufficiently alive to the importance of attending to the dif- 

 ferential motion, of determining the law of its variation from 

 molecule to molecule, and of ascertaining whether it is conti- 

 nuous or not. 



Observations of this kind are by no means easy to make, and 

 require to be conducted with great care and delicacy, errors which 

 might safely be disregarded in a determination of average daily- 

 velocity becoming serious when relative and not absolute motion 

 is the object of investigation. These errors arise from the diffi- 

 culty of boring with the augur vertical holes in the ice, of driving 

 the stakes vertically into the holes that have been bored, of re- 

 newing the holes in the same vertical when the glacier has melted 

 away from the stakes, and from the constant tendency of the 

 stakes to heel over to the southward in consequence of their 

 heated faces enlarging the holes in the direction of the sun. 



During a short tour in the Alps in the autumn of 1870, I 

 attempted, in concert with my friend Mr. A. Adams Reilly, to 

 make some observations upon differential motion, and selected 

 the side of the Great Aletsch Glacier as the field of our ope- 

 rations. 



By means of a well-defined station on the right bank of the 

 glacier, and a well-defined object on the left bank, we ranged out 

 a line between 60 and 70 yards long. We drove our first stake 

 into the ice 20 feet from the station, as near to the edge of the 

 glacier as we could conveniently get it. I shall denote this stake 

 by 0. We had intended to stake out the line every ten yards ; 

 but, from certain local difficulties, we were obliged to drive in 

 stake 1 at a distance of nine yards from 0. Stake 2 was eleven 

 yards from 1 ; and the remaining four stakes were placed at 

 successive distances of ten yards each. The line between and 

 1 was staked out into nine subdivisions of three feet each, and 

 the space between 5 and 6 into five subdivisions of six feet. 



Our work was completed in the afternoon of Monday, the 22nd 

 of August ; and the line was reexamined on Wednesday, the 24th, 

 after an interval of forty-eight hours. 



In the first place, the spaces between the stakes were carefully 

 remeasured, with the following results : — 



