32 Mr. C. Tomlinson on the Motions of certain 



lent" to that of Laplace, and infers that Laplace should have 

 come to the same conclusion. Without pretending to have formed 

 an opinion respecting the correctness of this inference, I venture 

 to say that the question admits of decision, apart from reasoning 

 with mathematical symbols, from this single consideration. So 

 long as the disturbing force tending to depress a given vertical 

 column of the fluid is diminishing, or that tending to raise it is 

 increasing, the length of the column is increasing ; but as soon 

 as the force ceases to increase, the raised column begins to de- 

 scend by the force of terrestrial gravity. Accordingly there will 

 be high water under the attracting body. It seems to me, after 

 consideration of the terms employed in the latter part of Cor. 19, 

 and especially of the meaning of the expression " usque ad qua- 

 draturas," that Newton intended to point out the kind of action 

 T have just described, which is, in fact, the same as that from 

 which he draws his conclusions in Prop. 36 of Book III. For 

 these reasons I am of the opinion that the above-mentioned con- 

 tradiction is due to fault or defect of principle in the method 

 of solution the Astronomer Royal has adopted. 



I think I am entitled to say that the solution of the problem 

 of the tides given in this communication, which differs materially 

 from that of Laplace, is the only one hitherto proposed that is 

 strictly based on the necessary principles of hydrodynamics. 



Cambridge, December 17, 1869. 



VI. On the Motions of certain Liquids on the Surface of Water. 



By Charles Tomlinson, F. R.S.* 

 1. TTPWARDS of thirty years ago I published 1 an account 

 vJ of some experiments on the action of vapours on films ; 

 and more than eight years ago some further results were given 

 in these pages 2 . For the sake of convenient reference I will 

 briefly recapitulate some of the leading facts. 



a. If a drop of ether, or a bit of sponge tied over the end of 

 a glass rod and dipped into ether, be held over the surface of 

 clean water, the surface just below the ether will be depressed 

 so as to form a cup-shaped cavity. 



b. If the water be dusted over with lycopodium powder and 

 the ether then held over the surface, the powder will be power- 

 fully repelled from the cavity. 



c. If the water be first covered with a film of oil, or turpen- 

 tine varnish, &c, and the ether-sponge be held over it, very fine 

 displays of Newton's rings will be produced. 



* Communicated by the Author. 



1 Student's Manual of Natural Philosophy (London, 1838), pp. 545 to 

 549, and pp. 553 to 555. 



2 Phil. Mas*, for August 1861. 



