Mr. Coorer’s Observations on Comets. 117 
eye end, which are covered with semi-transparent glass. This latter contrivance 
has been found of essential service in the observation of faint objects. The re- 
sults from the separate observations speak for the performance of the instrument. 
The observations with comet-seeker were in all cases taken with the steel 
bar micrometer eye-piece, power 30. The eye-piece commonly used in seeking 
for objects has a power of 23, as mentioned above. A power as low as 17 can 
be applied ; but it has been found to admit too much extraneous light, and, on 
the whole, not to be so satisfactory. The places of comets were, as usual, deter- 
mined by differences from some fixed star in the field, the circles of the instru- 
ment being merely used for identification of the star. The small stars observed 
with meridian circle were always taken in a dark field, with illuminated lines. 
The eight microscopes were read in most cases: when, however, want of time 
obliged us to take opposite readings with two microscopes, a correction was 
applied to reduce their mean to the mean of all. 
In reference to the table on page 119, after the numbers for reference, are 
given in the second columns the mean right ascensions and declinations for 1st 
January, 1846; in the third, the annual precessions in right ascension and de- 
clination ; the four following contain the constants for determining the apparent 
places of the stars by the methods now universally practised by astronomers ; the 
eighth column gives the number of observations; the ninth of Table I., the 
initials of the observers, myself and Mr. Graham ; the results of the separate 
observations have been annexed in the last column, when the same star was ob- 
served more than once. The transit corrections were determined from high and 
low stars, assuming the Nautical Almanac places to be correct. As the observa- 
tions for this purpose were generally made by Mr. Graham, it was found neces- 
sary to apply a correction of 0°.40 for personal equation to the transits taken by 
me, Viz. : 
EK. J. C.’s clock correction = A. G.’s—0°.40. 
The separate results, from the mean of which the position of the polar point on 
the circle was determined, are subjoined. These are generally by A. G. The 
refraction tables used here are those by Dr. Robinson, of Armagh. 
The succeeding tables require little explanation after what has been said. 
The longitude of this observatory from Greenwich has been taken at + 0” 33™ 
48°.4. It has been judged most convenient for all to give the mean Greenwich 
