142 Mr. H. H. Howorth on 



the tenth of an inch apart, and at an interval of 24 hours,, 



' from the gx^ to the ^oooq of an inch, while Mr. Moseley 



inferred the shearing force in ice to be 75 lbs., from 



experiments in which he caused a solid cylinder of ice to 



^ shear an inch in half an hour {PhiL Mag., XLII. 420). 



It was in 1870 that Mr. Matthews tried his famous 

 experiment upon the shearing of ice, which gave an entirely 

 different result to that of Mr. Moseley A plank of ice, 6 inches 

 wide 2^ inches thick, was sawn from the frozen surface of a 

 pond, and supported at each end by bearers 6 feet apart. 

 The whole weight of the plank could not have exceeded 

 2,7% lbs, and its cross-section was nowhere less than 14 

 inches. From the moment the plank was placed in position 

 it began to sink, and continued to do so until it touched the 

 surface over which it was supported. At the point of 

 contact it appeared bent at a sharp angle, and was perfectly 

 rigid in its altered form. The total deflection was 7 inches,, 

 which had been effected in about as many hours, under the 

 influence of a thaw, during which the plank diminished very 

 slightly in thickness. It was thus shewn that ice cans 

 change its form under strains produced by its own gravita- 

 tion \Alpine Journal, 1870, 426). 



The meaning of this experiment was very plain. Mr. 

 , Moseley himself says of this bending, "when the ice takes a 

 .distinct set, every particle, except those at the points of 

 support, is made to move in the direction in which the plate 

 is bent, those particles which are at the point of greatest 

 inflation being made to move furthest, and those nearer to. 

 ;it being always made to move further than those most 

 remote, so that every particle moves over that which is. 

 alongside towards the nearest point of support ; and being 

 assumed to have taken a set, it must have sheared over it."' 

 That is to say, the motion of the plank is precisely such a 

 .motion as Forbes's theory requires. Mr. Matthews pef- 

 tinently asks :— If the shearing force of ice be 75lbs. as. 



