6o 



NA TURE 



[Nov. 18, 1S80 



CC (see Fig. i) is a cylinder around vphich one thick- 

 ness of paper is wrapped, and underneath it is a long 

 screw WW. A wheel on the axis of c C gears into one 

 mounted on w w ; thus when the cylinder turns, the 

 screw turns, w w is tapped through the lower portion of 

 a carriage k (compare Fig. 2), and K rests on rails 

 parallel with w w. When the screw w w turns, k cannot 

 turn too, and is therefore propelled by the screw up or 

 down the rails underneath the cylinder. 



L is clockwork which drives the screw, and consequently 

 the cylinder and carriage. The rapidity with which l. 

 moves is regulated by the pendulum pp. p p is a conical" 

 pendulum ; that is, instead of oscillating, it swings round 

 in the surface of a cone. P P is suspended by two pairs of 

 springs S s, s s at right angles to each other. 



Let us consider the actions of c C and K (see Fig. 2). 

 K carries two prickers, one of which is placed in electrical 

 communication with the Observatory standard clock. It 



is so arranged that at every beat of the standard clock 

 (except the 60th second of each minute) the pricker shall 

 rise and puncture the paper wrapped round the cyUnder. 

 Now suppose that whilst the clock keeps pricking, the 

 cylinder is turning, and the carriage K moving to the left. 

 Then we shall get a succession of pricks marked off upon 

 the cylinder in the form of a slightly inclined spiral, and 

 the distance between each prick will represent one second. 

 Every 60th prick (or second) being omitted, the occurrence 

 of each minute is easily distinguished. 



The carriage K carries another pricker alongside the 



clock-pricker — this is the observation-pricker. The 

 observation-pricker is placed in electrical communication 

 with any instrument in the observatory the astronomer 

 may be going to use, and it is so arranged that the astro- 

 nomer by merely pressing down a stud can cause the 

 observation-pricker to rise and puncture the paper on the 

 cylinder. This it will do somewhere alongside the spiral 

 of clock-pricks. By reference to the latter the time of the 

 observation can then be determined to the ?^^\.\\ of a second. 

 Let us examine the pricks on the cylmder (Fig. 2). 

 The spiral of the clock-pricks winds around the cylinder 



