346 



nel, in which it is no longer influenced by the forces of the moon and 

 sun, it would take a certain time in reaching any place in that chan- 

 nel, and the circumstances of the tide at that place would not depend 

 on the positions and distances of the moon and sun at the time when 

 the tide happens, but on the positions and distances of those lumina- 

 ries at a certain time, anterior to the time of the tide, by the interval 

 occupied in the transmission of the tide along the channel. This in- 

 terval of time, which, in his former papers, the author had called the 

 age of the tide, he here terms the retroposition of the theoretical tide 

 in time. 



Adopting this phraseology, the author finds that the phenomena of 

 the Liverpool tides may be expressed as follows. 



1. The effects which the changes of the moon's force produce on 

 the tides are the same as the effects which those changes would pro- 

 duce upon a retroposited equilibrium tide. 



2. The retroposition of the tide in longitude is affected by small 

 changes, which changes are proportional to the variations in the moon's 

 force. 



3. The retroposition of the tide in time is also affected by small 

 changes, which changes depend on the variations in the moon's force. 



On the hypothesis that an equilibrium tide give rise to the Liver- 

 pool tides, we must suppose that the channel by which they are trans- 

 mitted occupies in length, from west to east, 1 1 h 6 m of longitude ; or 

 we may suppose the tide spheroid to lie behind the position of equi- 

 librium by a certain space j and the longitude occupied by the chan- 

 nel from end to end, may be supposed to make up the rest of the ll h 

 6 m , the retroposition of the tide in longitude. The author proceeds 

 to show how the circumstances of the tide may be hypothetical ly re- 

 presented on these suppositions ; although it is not to be imagined 

 that these hypotheses are strictly accordant with the true state of the 

 case. As the general laws of the tides at other places must resemble 

 those at Liverpool, they will of course be capable of being represented 

 in a similar manner. 



The remainder of the paper is occupied by a comparison of the data 

 of observations at London and Liverpool, and by an investigation of 

 the corrections in the formulae thence resulting. 



November 26, 1835. 



Sir JOHN RENNIE, Knt. Vice-President, in the Chair. 



Robert Alexander, Esq. j Charles Elliott, Esq. j and Sir William 

 Molesworth, Bart., M.P., were elected Fellows of the Society. 



ei Observations on Halley's Comet, made at Mackree, Sligo, in the 

 Months of August, September, October and November 1835." By Ed- 

 ward J.Cooper, Esq. Communicated by Capt. Beaufort, R.N., F.R.S. 



These observations are communicated in the state in which they 

 were taken, and without the corrections for refraction and parallax, 

 with a view to assist computers in the calculation of a new approxi- 



