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V.— Observations on Comets, made at the Observatory of Markree, during the 
first six Months of the Year 1846. By Epwarp Cooper, Esa. 
Read 20th July, 1846. 
THE instruments employed in making the following observations were a comet- 
seeker and meridian circle, both by the Ertels, of Munich; and as the works of 
these distinguished artists are little known in this country, and appear to me of 
very superior construction, a brief notice of them may be acceptable and useful. 
The base of the comet-seeker is a strong, conical, brass column, supported by 
a nearly horizontal tripod, with adjusting screws to set it vertical. There is an 
azimuthal motion, with clamp and opposing tangent screws, for the purpose of 
placing the polar axis in the meridian. It bears a strong brass prism, carrying at 
the eastern side one of Frauenhofer’s clocks, for moving the telescope ; at the 
other, a level, to watch the permanence of its position. The southern face of the 
prism is inclined at an angle approximately equal to the latitude of the place ; 
but, for accurate adjustments, a strong plate of equal dimensions, and to which is 
attached the brass-work carrying the polar axis, lays over this face, having no 
actual contact with it. Across the lower part of the face of the prism is attached 
a small cylindrical steel rod, adapted to which is a groove in the under surface of 
the strong plate. There are four screws for connecting this plate with the prism; 
and besides, two pressure screws at the upper part of the plate, by which the 
upper end can be raised or depressed, while the groove in the under part of the 
plate works upon the cylindrical steel rod on the face of the prism. The polar 
axis is of steel, conical, thirteen inches long, and turns steadily and smoothly in a 
strong tube attached to the plate which I have described, the friction being les- 
sened by a counterpoise, applied as in the Dorpat and Konigsberg equatorials. 
The lower extremity of the axis carries the hour circle, 84 inches diameter, and 
