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THE POPULAR SCIENCE MONTHLY. 



apparatus, and being further corrected daily by the adjustment of 

 weights to the pendulum. For the latter purpose the pendulum-rod 

 is provided with a box, c (Fig. 1), for holding small weights ; these 

 are made of such shape that they can be easily put into the box or 

 taken out by means of a small pair of pincers without in any way 

 affecting the running of the clock. The box being placed above the 

 center of oscillation of the pendulum, the addition of a weight makes 

 the clock go faster and the removal of a weight retards it. By re- 

 peated experiment it has been ascertained what change each weight, 

 under given conditions of atmospheric influences, will produce in a 

 given time ; so that the operator knows how to adjust the weights in 

 every case, and the clock can be kept running on mean time with 

 the greatest attainable accuracy. 



This clock, beating seconds, closes for, say, one half second during 



each vibration an electric cir- 

 cuit along the line of which the 

 secondary clocks are situated. 

 This is done by means of the 

 apparatus shown at the top of 

 Fig. 1. To the upper end of 

 the pendulum-rod are attached 

 arms, V and V, which alter- 

 nately raise the levers, i and i\ 

 as the pendulum vibrates, thus 

 closing the contact of the elec- 

 trie circuit, one wire of which 

 reaches the arms V and V, 

 while the other is attached to 

 the levers i and i'. There are 

 three levers at i and i', and 

 three contact points on the 

 arms V and V, in order that 

 the transmission of the current 

 need not depend upon a single 

 contact which some trivial cir- 

 cumstance as, for example, the 

 lodging of a grain of dust 

 might prevent. 



The current thus transmitted 

 is carried laong wires placed in 

 the city drains to the secondary 

 clocks, which are controlled by 

 the regulator at the observatory, as shown in Fig. 2 ; but the motive- 

 power of each is a weight operating as in ordinary clocks. To the foot 

 of the pendulum of each secondary clock is attached a piece of soft 

 iron, which swings just above the poles of two electro-magnets in the 



Fig 2. Psndut.um of Sixondatiy Clock. 



