148 Royal Society. 
val of time, which, in his fermer 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, 11" 6™ of longitude; or 
we may suppose the tide spheroid to lie behind the position of equi- 
librium by a certain space; and the longitude occupied by the chan- 
nel from end to end, may be supposed to make up the rest of the 115 
6™, the retroposition of the tide in longitude. The author proceeds 
to show how the circumstances of the tide may be hypothetically 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 formule thence resulting. 
November 26, 1835.—‘‘ Observations on Halley's Comet, made at 
Mackree, Sligo, in the Months of August, September, October and 
November 1835.” By Edward 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- 
mate orbit. They were made principally with the author’s equatorial 
telescope, having a focal length of 25 feet 3 inches, and a clear aper- 
ture of 13°3 inches. Some few, however, were taken with the finder, 
which is 6 feet 6 inches in focal length, and 4-9 inches clear aperture. 
The eye-pieces used were, one by Frauenhofer (an illuminated wire- 
micrometer), one by Messrs. Troughton and Simms (an illuminated 
field-micrometer), a comet eye-piece, and the ordinary eye-piece of 
the finder. The first of these had a magnifying power of about 400, 
the second of 226, the third of about 95, and the fourth about 40. 
«An Account of the great Earthquake experienced in Chili, on the 
20thof February 1835,” withaMap. By Alex. Caldcleugh, Esq., F.R.S. 
An idea formerly prevailed among the inhabitants of Chili, that the 
earthquakes of those regions take place at certain regular periods ; 
but it is now sufficiently proved, from the numerous catastrophes of 
this kind which have occurred during the present century, that they 
may happen indiscriminately at all times, and in all states of the at- 
