414 



Mr. W. Parkes on the Tides of 



[May 28, 



collision may occur, viz. the instantaneous transmission of a finite amount 

 of momentum from one part of the system to another, provided we have 

 discontinuity in the tendency to compression in the different parts of the 

 system. 



The author has endeavoured, in former communications to the Royal So- 

 ciety, to show that when the velocity in a fluid diminishes in the direction 

 to which the motion tends, the slower particles will offer a resistance to the 

 motion of the faster particles, which the received theory fails to take into 

 account. The foregoing speculation goes to prove that the circumstance 

 of the surfaces of contact of contiguous elements of the fluid having the 

 same velocity, constitutes no objection to the reality of such resistance. 



IV. ^' On the Tides of Bombay and Knrrachee.'^ By William 

 Parkes^ M Jnst. C.E. Commnnicated by G. B. Airy_, Astro- 

 nomer Royal. Received May 5_, 1865. 



(Abstract.) 



The object of this paper is to exhibit the phenomena of diurnal inequality 

 in the tides on the coasts of India, and describe the mode adopted by the 

 author for obtaining formulae based on astronomical elements for predict- 

 ing them. It is accompanied by the following records of observations given 

 in a diagram form : — 



Kurrachee, 1857-8, December to ]March. 



„ 1865, March to August. 



„ 1867, The whole year. 



Bombay 1867, February to May. 



The height and times predicted by the author for 1867, and published 

 by the India Oflice, are given on the diagrams for that year, so that they 

 may be compared with actual observation. 



The continuous curves of the height of the water taken at Bombay, at 

 every ten minutes for the four months above named, are also given. 



By the rotation of the earth every meridian-line is brought twice a day 

 under the influences which ultimately result in the well-known semidiur- 

 nal tidal movements — once when in the position nearest to the attracting 

 body, and once when in that furthest from it. But the actual point hi 

 that meridian which is in the centre of those influences will be alternately 

 north and south of the equator, to the extent of the dechnation of the 

 attracting body. This alternation of the position of the centre of attrac- 

 tion from the northern to the southern hemisphere produces a diurnal 

 tide, and that diurnal tide produces a diurnal inequahty in the semidiurnal 

 tide 



