34 Mr Skinner, On Cavitation in Liquids, 



On Cavitation in Liquids, and its Occurrence in Lubrication. 

 By S. Skinner, M.A., Christ's College. 



[Read 10 November 1902.] 



If water is run into the space between two lenses, arranged so 

 as to shew Newton's rings, and if one of the lenses is rolled on the 

 other a crescent-shaped cavity is developed when the velocity of 

 rolling exceeds a certain critical value. The cavity fills as soon as 

 the rolling ceases. With more viscous liquids, such as lubricating 

 oils or glycerine, the formation of the cavity is more marked. 

 With colourless liquids the production of the cavity is observed 

 by taking advantage of total internal reflection, or by using sodium 

 light and observing the Newtonian rings formed in the cavity. 

 With deeply coloured liquids the effect may be observed by 

 transmitted light. Instantaneous photographs have been obtained 

 of the effects with lenses rolling on planes, cylinders on planes, 

 lenses sliding on planes, and in some other cases. The effects are 

 shewn to agree with Osborne Reynolds' theory of the viscous 

 origin of friction when copiously lubricated surfaces move over one 

 another {Phil. Trans. A, 1886). That the maximum negative pres- 

 sure occurs at some distance from the point of nearest approach is 

 confirmed by these observations, and it appears that the layer of 

 lubricant which separates the surfaces at the point of nearest 

 approach is thinner than the wave-length of sodium light. Cavities 

 of the same character probably occur in all sufficiently lubricated 

 bearings. 



[Note added 20 December, 1902. When the above paper was 

 read before the Society I had only consulted certain reprints of 

 Newton's Optics, and I was surprised that there was no mention 

 of the formation of the cavity in the experiment which he made 

 with water between the lenses. I now find that in Observation 11 

 he did notice the cavitation of the water but he did not go 

 further with the observation. He supposes the cavity to be filled 

 with a subtile medium which passes through the glass when the 

 water creeps in. The following is quoted from the Third Edition, 

 published in 1721, of Newton's Opticks, Second Book, part I. 

 page 183. 



