IX.—PLACES OF ONE THOUSAND STARS OBSERVED AT THE 
ARMAGH OBSERVATORY. By Rev. THOMAS ROMNEY ROBINSON, 
DD, Ti IBy5 WAC ys Mba one 
[Read January 2Ist, 1878] 
TuE observations, on which the present catalogue is based, were made with the 
Armagh Mural Circle, described in the Transactions of the Astronomical Society, 
Vol. [X., and in the preface to the Armagh Star Places. It was constructed with a 
view to its possible employment as a transit instrument, having cylindric pivots turn- 
ing in Ys of 60°. However, it was not so used till I formed the plan of re-observing 
those of the smaller stars of the LHvstoire Céleste which had not been recently 
determined. For this work the Armagh instruments were scarcely adequate from 
the small size of their object glasses (3°75 aperture), which in the atmosphere of 
this island has often too little ight to show faint stars. It was impossible to fit a 
larger one to the transit instrument; but with the circle it was possible, and the 
liberal bounty ef the late Primate, Lord John Beresford, enabled me to effect it. 
A new telescope was attached to the steel axis which carried the old one; it was 
eighty pounds heavier, but the effect of this was obviated by altering the counter- 
poise and adding another to the end of the axis, so as to keep the C. G. of the in- 
strument still in the plane of its friction-wheels, . 
The arrangements of the room required that its focal length should be nearly the 
same as that of the old one; it is 68 inches, but its aperture is 7” clear. It was 
made by Mr. Grubb, F.R.S.; and its object glass is peculiar. It consists of two 
achromatic lenses, each cemented, so that there are only four reflecting surfaces, 
as in ordinary objectives, and the glasses are of remarkable transparency. ‘The 
definition and light are excellent. To its north and south two collimators are fixed 
on insulated pillars, which, when the telescope is vertical, see each other through 
apertures in it (ordinarily covered by pieces easily removed). The collimation is 
very permanent. The level is got by observing the reflection of the wires. If the 
direct and reflected images of the centre coincide, level is right; if they do not, the 
error is measured thus:—A draw-tube of the eye-piece contains a double-image 
prism, and carries a divided circle whose verniers read 90° when the wires appear 
single; then by turning the tube till the direct and reflected images coincide the 
level error is 4X16". 94xcos @ Azimuth error can be similarly measured from 
the meridian mark. 
