Five-feet Equatorial Instrument. 9 
declination axis. There is a neat contrivance placed between 
the nosel of the lantern and end of the axis, by which the 
quantity of light is regulated, so as to suit the nature of any 
observation that may be made ; and such is the amplitude of 
this illumination, that, on one hand, the brightness of broad 
day is produced, and on the other, total darkness. In any 
position of the telescope, and while the object is viewed, the 
adjustment of light can be conveniently effected, by means of 
a long handle shown in Plate I. fig. 1, hanging down on the 
hither side of the polar axis. 
In Plate III. fig. 4, the eye-piece of the telescope is repre- 
sented, in which there is seen the edge of a graduated circle, 
the front of a quadrant, and two small spirit levels. This ap- 
paratus is particularly described by Sir G. Shuckburgh, in the 
Phil. Trans. 1793 ; by which, and by some small tables given 
in his paper on the Equatorial, the corrections due to refraction 
and parallax are neatly allowed for, in observations made at 
a distance from the meridian. There is also seen in this 
figure, rather partially represented, a double parallel line mi- 
crometer (sometimes called a repeating micrometer), which 
also measures angles of position. Although this apparatus 
has had not a little to do with the observations recorded in 
this paper, it is forborne to give a detailed account of it : 
1st., because it would considerably lengthen this description, 
which, it is feared, many will think too long already ; edly, 
because a great number of these micrometers are in the pos- 
session of practical astronomers, and of course their con- 
struction is tolerably well known ; and, lastly, because they 
have been described in our modern Encyclopasdias.* It is 
* Rees’s Encyclopaedia, Article Micrometer. Brewster’s ditto, ditto- 
MDCCCXXIV. C 
