4 Reynolds, On the. Slipperimss of Ice. 



theory of lubrication * showing that not only in the case 

 of the oil-bath, when the thickness of the separating film 

 of oil was about 2/i,oooth of an inch, but in cases of 

 ordinary lubrication where the thickness of the film is 

 less than 'oooi of an inch, the surfaces are separated by a 

 complete film. 



This is very strikingly indicated by a rarely shewn but 

 simple experiment. Two cylindrical hard steel gauges, 

 male and female, one inch in diameter, made to gauge to 

 within I /20,000th of an inch will not pass one into the 

 other, if wiped as clean as possible of all oil, without the 

 use of great pressure or of a mallet. If oiled and kept 

 moving they can be easily passed one into the other. 

 But should the motion be arrested for a second, they seize 

 and can only be separated by the mallet, which shows 

 that a film of oil less than the i /20,000th of an inch is 

 suf^cient to sustain perfect slipperiness, while the least 

 contact destroys this property. 



My research also led to the recognition that the 

 property on which the lubricating action depends is the 

 viscosity of the fluid, and that all fluids are lubricants, 

 provided they are not corrosive. Air lubricates, as is 

 shown by the floating of one true surface plate on another 

 with perfect slipperiness. Now water had, at the time, 

 not been recognised as a lubricant ; its viscosity is from 

 200 to 400 times less than oil, but from my research it 

 appeared that it is a lubricant in proportion to its 

 viscosity. 



All this is now matter of history, and its bearing on 

 the slipperiness of ice may not as yet be clear. But it has 

 a fundamental bearing nevertheless. 



It was about 1886, while I had this subject of lubrica- 

 tion very fresh in my mind, that I was, for some reason, 



* Phil. Trans. 1880, Part I., pp. 157 — 234. 



