454 Scientific Proceedings, Royal Dublin Society. 



the pressure will rapidly attain the inoperative intensity, so that it 

 will be found difficult to obtain bite — a state of things skaters are 

 familiar with. But it would appear that some penetration must 

 ensue. On very cold ice, " hollow- ground" skates will have the 

 advantage. 



This explanation of the phenomena attending skating assumes 

 that the skater, in fact, glides about on a narrow film of water, the 

 solid turning to water wherever the pressure is most intense, and 

 this water, continually forming under the skate, probably resum- 

 ing the solid form when relieved of pressure. From the thermo- 

 dynamic point of view, the skater is the external agent, putting the 

 ice through a reversed Canot's cycle. Fluid shearing takes the 

 place of solid friction, and as the resistance thus arising is propor- 

 tional to the area over which shearing obtains, that temperature at 

 which the skater just obtains the requisite bite to impel himself 

 will be the most conducive to freedom. Other phenomena, such as 

 tearing and crushing, doubtless attend the skater's motion, but 

 such must necessarily be detrimental to freedom ; indeed, the fact 

 that such phenomena do often attend the easy motion of the 

 skater might be regarded as evidence against the popular notion 

 that the possibility of skating is to be ascribed solely to the smooth- 

 ness of the ice. It is quite certain, I think, that skating on so 

 smooth a substance as plate-glass, for example, more expecially if 

 accompanied with incidental tearing of the surface, would be quite 

 impossible. Again, it is observable that skating on very rough 

 ice is possible. Only, indeed, when the phenomena of solid fric- 

 tion give place to those attending the motion of lubricated surfaces 

 is there at all a comparable degree of freedom. Walking on a 

 pavement greasy with fine mud occasionally recalls the accidental 

 treading on a " slide." 



In the expression " as slippery as ice " there is revealed a con- 

 sensus of opinion as to the abnormal nature of ice respecting 

 friction. 



