ON Tin: M'.i.ri.rs OF TMI:M>\\I. I.-HJIDITY OF MKTAL WIKF.S. n 



nearly .MI exact multiple of this time. Considering the fractional part only, put 

 I I . : )4 x P = Q, whence n l' = iVbVo successive convergents to which are , , -ft, ^. 

 Hence tin- mmil>eis which multiplied by 4'1 154 give products nearest whole numlH-rs 

 IK- 8, 9, 17, 2G. . . The larger the factor the nearer is the product to ;i whole 

 number, and at first sight it might aBem to Ke of advantage to use the largest to obtain 

 tin- coincidence period, but taking 'JO we li;i\e L'G X 4'1154 = 107D004, so that in 

 a period of 107 seconds the vibrator will have "lost" '0004 second, and therefore to 

 lose 1 second it will take 2500 periods of 107 seconds, or over 70 hours! In the 

 present instance 9 is the most suitable factor and gives 9 X 4'1154 = 37'0386, so that 

 in a period of 37 seconds the vibrator lags behind by '0386 second, and therefore 

 " loses" 1 second in 10 minutes. 



Tit* Flashing Apparatus. 



The second signals are given by a clock pendulum, carrying at its lower end a 

 platinum wire, which cuts through a fine stream of mercury each time the pendulum 

 passes its position of rest. This "makes" a circuit, which by means of a relay 

 "breaks" another circuit through tin- primary of an induction coil, thus giving a 

 flash in a vacuum tube connected to the secondary circuit. The platinum wire is 

 flattened out perpendicularly to the plane of swing of the pendulum. It is 6 millims. 

 long and is screwed into a small brass pin, which fits into a hole in the lower end of 

 the pendulum, being secured in position by a screw. It can easily l>e removed for 

 cleaning. This brass pin is joined to a fine copper wire running up the back of the 

 wooden pendulum rod and connected at the top to the lower end of the steel strip by 

 which the pendulum is suspended. The pendulum suspension is connected by ;i win- 

 to a terminal screw outside the clock case. 



The stream of mercury issues from a very fine glass jet fixed to the back of the 

 clock case. An adjustment in the position of this jet can be made by means of t\\<- 

 large milled-headed screws, so as to direct the stream exactly through the position of 

 the platinum wire when the pendulum is at rest. The jet is at the end of a glass 

 tube which enters the case through a hole in the side, and is bent so as to direct tin- 

 stream of mercury perpendicularly to the plane of swing of the pendulum. This tuU- 

 is connected by indiarubber to a reservoir containing some 500 cub. centims. <>l 

 mercury, at a level of about 30 centims. alxwe the jet. The rate of flow of the 

 mercury can l>e regulated by a stop-cock. In the glass tube, just before the jet, are 

 two air traps, in order to stop any bubbles of air which might interrupt the mercui v 

 si i earn. A platinum wire, connected outside to a terminal, is also sealed into the 

 tu!>e to make contact with the mercury. The mercury running from the jet is 

 collected in a wooden box from which it can be drawn oft' and returned to tin- 

 reservoir. 



The clock break is connected in series with two accumulator cells and a contact 



C 2 



