149 Transactions.— Miscellaneous, 
Fig. 1 represents the field of view of a positive eye-piece of high mag- 
nifying power. In this are arranged, in the manner shown in the figure, 
images of wires for ordinary use and of webs for more delicate observations. 
Fig. 2 is the position circle. This is made of very stout block-tin, and 
is wired at the back to prevent its warping. Its circumference is divided 
into degrees (the minutes are to be estimated). The circle is fastened on & 
central cap, like that which is used for a sun-shade, so that the circle can be 
screwed on to the eye-piece with facility. Every care must be taken to set 
the plane of the circle at right angles to the axis of the telescope. 
Before the circle is put on the eye-piece, the index I, fig. 3, is placed 
on the telescope, tube T’, and temporarily secured by means of the clamp 
and screw Cs. Then the circle is put on, and the apparatus will be in 
the condition represented in fig. 8. If the telescope used is equatorially 
mounted and properly adjusted, it may be now turned on a double star in 
any part of the heavens; if it is an alt. azimuth, a star must be chosen on 
or near the meridian, the nearer the better. The star, or rather one of the 
component stars, is now made tó run along between the wires TT, fig.1, by 
turning the eye-piece tube of the telescope round until it does so. Then 
the index I, fig. 8, must be made to point accurately to the zero of the 
position circle, and be firmly secured there by means of the clamp. 
Next the eye-piece tube is turned round until the line joining the centres 
of the two stars is exactly parallel to the two wires. Then the circle 
indication is read off, and, if necessary, 180° must be added to the angle so 
obtained. Then, evidently, the angle of position with the meridian has 
been obtained. Several observations of the same star on different nights 
should be taken. It is advantageous, too, to use different parts of the circle 
as the zero point. If this be done, the mean of all the observations will be 
a very close approximation to the truth. 
Having found the angle of position, we next proceed to obtain the 
distance. This operation should be attempted only in the very finest 
weather. The writer always measures distances either in morning or 
evening twilight, or in full moonlight when the moon is near the meridian. 
Thus the illumination difficulty is avoided. 
The clepsydra, the use and construction of which will easily be under- 
stood from the section of it given in fig. 4, is placed in a convenient position 
near the telescope. The tanks T and T” are filled with water, the eyepiece 
tube is turned round as in the previous operation. until one of the com- 
ponents of the double star runs along the wire TT or the web w.w. Then 
the star is recalled and raised in the field a litttle, so that it may transit the 
oblique wire TW, or the oblique web w.T. The instant that the first star 
is bisected by the wire or web, the lever is pressed sharply down to the peg P 
