Mr. Coorer’s Observations on Comets. 115 
reading with two verniers to four seconds of time. The upper extremity has, 
first, the apparatus for clock and screw movement; second, the transverse socket, 
in which the cylindrical declination axis turns. This bears the telescope at one 
end, 3.8 English inches aperture, and 31 inches focal length. The magnifying 
power in general use for sweeps is 23, and the field about 2°8’. The glasses are 
by Merz, and define very sharply; the lines in its focus are illuminated in the 
ordinary way. At the other end of this axis is the declination circle, ten inches 
diameter, and reading with two verniers to minutes of space. Here also are fixed 
the tangent screw and clamp, the socket bearing a counterpoise merely to equili- 
brate the telescope, any contrivance for lessening the friction being unnecessary 
here. It is usual to have an apparatus for illumination of the lines in a dark 
field, but there are many comets too faint to bear even this, and by many the 
circular micrometers of Valz and others are used. I, however, prefer one of the 
ordinary construction, in which bars of steel are substituted for the spider lines, 
whose edges are exactly parallel. Three of these, being placed equidistant, serve 
to take the transits by a mean of the disappearance and re-appearance of the 
object, and two at right angles to them, moveable by micrometric screws, give, 
in the same way, differences of declination. The breadth of the bars is five 
minutes of space, and they are always visible without extraneous illumination. 
The perfect finish of this instrument has excited the admiration of all who have 
seen it; and I am of opinion, that, with a finer division of its circles, it might be 
recommended to amateur astronomers as capable of rendering to their science the 
greatest amount of service which can be obtained by an ordinary sacrifice of time 
and money. It stands in a small observatory, connected with the circular enclo- 
sure of my great equatorial, and level with its summit ; it rests on an insulated 
pular, and is covered with a moveable dome. ‘The room is entered from the re- 
volving gallery within the enclosure. 
The German meridian circles are now well known by the labours of Bessel, 
Struve, Schumacher, and others. In the British dominions it has been the prac- 
tice to prefer the combined use of the transit instrument and mural circle, which 
causes a great increase of expense, and requires two observers. These may not 
always act simultaneously ; and it is seldom that two persons meet whose vision is 
similarly affected internally from their natural constitutions, or externally from 
atmospheric influences. The Munich circle does the work of both; its action as 
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