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XIII. The Influence of Pressure on the Surface Friction 

 of Ice. By Henry Morphy, B.A* 



THIS investigation was undertaken at the suggestion of 

 Dr. Joly, who thought that it might be o£ interest in 

 connexion with his theory of skating. This theory being, as 

 is well known, that skating is rendered possible by the 

 formation of a film of water, between skate and ice, owing to 

 the melting of the latter under pressure. 



The experimental determinations consisted in the measure- 

 ment of the coefficient of statical friction between the runners 

 of a small sleigh, carrying a variable load, and the surface 

 of ice kept at constant temperature. 



In some preliminary experiments difficulty was encountered 

 in measuring the correct surface temperature of the ice, 

 which was formed in a shallow trough, surmounting a flat 

 copper box, through which a current of freezing-mixture was 

 passed. With this apparatus it was impossible to eliminate 

 surface radiation, and hence, owing to the blanketting effect 

 of the sleigh, the temperature beneath its runners would 

 vary. As it was desirable to know definitely the surface 

 temperature of the ice and essential to ensure its being dry, 

 this apparatus was abandoned and the following, in which 

 the ice was formed in a constant temperature enclosure, was 

 adopted. 



A glass gas chimney 8 inches long by 2 inches diameter was 

 closed at the ends with rubber disks covered by brass disks 

 which were bolted together by two long tie-rods, passing 

 through lugs in the brass. Through the centre of one brass 

 disk a ^-inch brass tube 8 inches long was soldered, being 

 flush with the inner side of the brass. A piece of ^-inch brass 

 tube was similarly fitted into the same disk close to the larger 

 tube. These two tubes were cemented into a circular disk of 

 pitch pine 5 inches in diameter, leaving 4 inches between 

 brass disk and wood. This wooden disk enabled the whole to 

 be fastened into the constant temperature enclosure, which 

 was simply a rectangular box of pitch pine, fitted with glass 

 windows for purposes of observation, and having two brass 

 tubes for the circulation of the freezing-mixture. This box 

 was placed on a platform which could be tilted to any angle. 

 Horizontal and vertical scales enabled the tangent of the 

 angle to be read. 



A small sleigh was made from sheet aluminium, having 



* Communicated by Prof. Joiy, F.R.S. 



