!_' DR. F. HORTON ON THE EFFECTS OF CHAM'.l.s OF TKMPKI!ATri;i; 



breaker, shown in fig. 3. The wires from the clock are connected to the terminals 

 of the small electromagnet A. Every second this becomes excited and attracts a soft 

 iron armature, B, which is fixed to the shorter arm of the light brass lever <J. This 

 lever is 18 centims. long and the short arm is 2 '5 centims. To the longer arm two 



Fig. 3. 



platinum wires are brazed, one at D and the other at E. The wire at D dips into a 

 mercury cup, F, and is not drawn out when the magnet is excited. The wire at E 

 dips into another cup of mercury, H, and the position of the lever is so adjusted, 

 by the two stops K and L, that E is drawn well out of the mercury in H when the 

 clock circuit is made. The terminals M and N are connected to the mercury in the 

 cups F and H respectively. Wires from them go to the primary of the induction 

 coil, two accumulator cells being included in this circuit. The contact breaker on 

 the induction coil is tied back so that it cannot work, and hence once a second the 

 primary circuit is broken and a flash occurs in the vacuum tube connected to the 

 secondary. 



At first a layer of water was kept over the surface of the mercury in H, but after 

 a time this became very dirty (the " dirt " being probably a platinum amalgam ,in a 

 very fine state of division) and a skin formed on the surface of the mercury. This 

 led to the circuit sparking two or three times .at each break, and caused much trouble, 

 for the result is two or more flashes in the vacuum tube (not separately visible), and 

 therefore two or more in different parts of the field of view of the telescope. In 

 order to overcome this difficulty, the arrangement shown in the figure was used. 

 The cup H was made by blowing a hole in the side of a bulb blown in a glass tube, 

 one end of which was then bent up (P) and the other slightly down (Q). The 

 mercury in H does not come up to the level of these side tubes. P is connected to 

 the stop-cock of a vessel containing water and Q hangs over a bucket. The water 

 flows slowly into H and its level gradually rises until the extra pressure is sufficient 

 to overcome the surface tension of the drop which always hangs from Q. It then 



