644 



Scientific Proceedings, Royal Dublin Society. 



Bound a pivot X fixed in NO rotates a slotted piece R, which 

 can he clamped at U to the disc V, the edge of which disc is 

 graduated in degrees. A pointer Q is attached to the piece NO. 



Fig. 2. 



P is a cylindrical pin passing through R at right angles. Finally 

 ST is a straight edge, which is always at right angles to YZ (or to 

 AC, fig. 1), along which it slides. 



Now in fig. 1 the angle between 10 and GL is + h. Accord- 

 ingly, by causing the direction of the zero of the graduation on V 

 (fig. 2) to make an angle with that of R, the pointer Q reads the 

 altitude directly. 



To find the Altitude of a star, therefore, it is necessary to set 

 NO to the declination. Unclamp U, and bring P up to the point A 

 (fig. 1). Clamp U. Slide ST along YZ till it cuts the circle M at 

 the hour-angle. Rotate R tillP touches ST. Then the pointer Q 

 reads off the altitude. 



