352 Proceedings of the Royal Physical Society. 



adopted by them since I suggested it some time ago. The 

 arrangement is seen in PL XV., Fig. 1. The small electro- 

 magnet is fixed on a brass plate, and draws down an arma- 

 ture carried by one end of the short lever. This is pulled 

 away again by a spiral spring seen in front of the pillar. 

 The other end of the lever ends in a binding screw, through 

 which passes a thin wire about 3 in. long. This wire is bent 

 at its further end in the way seen in the figure, and serves 

 as the means of attachment of a piece of fine vaccine tube 

 bent at right angles, the point of the horizontal half of which 

 presses on the paper. The vertical arm of the tube dips into 

 a brass cup carried at the end of another wire which passes 

 through a hole in the pillar, in which it is secured by a 

 pinching screw. This cup is filled with ink, which flows by 

 capillarity along the tube, and runs steadily out on the 

 moving paper. The most convenient way of fixing the 

 vaccine tube to the wire is by means of one or two turns of 

 fine silver suture wire. If thread is employed it is apt to 

 tighten when wet, and often snaps the tube. Such an 

 arrangement will work continuously for many hours with no 

 further trouble than the occasional supply of a few drops of 

 ink to the cup. If smoked paper is to be used, it is only 

 necessary to remove the cup and ink tube and attach a wire 

 carrying a sharp writing point to the binding screw on the 

 lever. 



4. Laboratory Clock. 



I have had a simple form of laboratory clock constructed 

 which has proved satisfactory and convenient. 



The clock is driven by a spring acting on a train through 

 a fusee, and is thus regular for all states of the spring. The 

 pendulum is a half-seconds one, and the dial is divided into 

 thirty divisions, and is traversed by the pointer once in 

 fifteen seconds — one division corresponding to half a second. 



Across the frame of the clock, behind the works, a narrow 

 wooden bar is fixed, through a slot in which the pendulum 

 rod swings (PL XV., Pig. 2). The rod is of brass, and 

 carries a brass block at its middle point, the lateral surfaces 

 of which are covered with platinum. On each side of the slot 

 a brass pillar carries in a vertical position an exceedingly 



