THE ROYAL ARTILLERY INSTITUTION. 
157 
Regulating the Currents.* 
11. The communications having been established, the disjunctor is put 
upon cock, and the operator, by touching the two straight electro-magnets 
with a piece of iron, assures himself that the currents follow the required 
circuits. If he finds that both magnets are active, he is certain that this is 
the case; if one, or both of them, are not active he knows that there is a 
breakage somewhere in the communications, or that the batteries do not 
furnish a current of sufficient intensity. Supposing that both magnets be 
found active, the operator then causes the pendulum to oscillate, and 
proceeds to regulate the mercury in the little iron cup of the conjunctor, by 
turning the vertical screw-head till the mercury comes in contact with the 
point of the pin belonging to the steel blade ; the moment the mercury 
touches the pin the third circuit is completed, the large horseshoe electro¬ 
magnet becomes active, and, by exerting a greater force upon the washer of 
the needle than the spring which presses this washer to the pendulum rod, 
clamps the needle. 
The operator then turns the vertical screw-head back two whole revolutions, 
so that the circuit is again opened, the washer now is detached from the 
electro-magnet by taking its collar with the forefinger and thumb, and drawing 
it towards the operator's body. 
12. These preliminary arrangements being completed, the pendulum is 
carefully raised to its initial position, supporting the rod on the first finger. 
If the pendulum bob is attracted very strongly , the battery must be reduced 
one element, by changing the points of attachment of the wire, Pig. 6. 
The power of the electro-magnet is again 
tested,and the core withdrawn till the electro¬ 
magnet has not the power of holding the 
bob any longer, the core is then screwed back 
till the magnet just holds up the bob. 
The core or piece of soft iron in each of 
the two straight electro-magnets is made to screw in and out, by this means 
the power of the magnet can be varied at pleasure. 
13. Exactly the same arrangements are gone through in regulating the 
currents of the conjunctor, whose electro-magnet is just made powerful 
enough to overcome the effect of gravity, and hold up the leaden weight. 
Trial of the Apparatus when Adjusted. 
14. When the apparatus has been thus adjusted, a trial is made to see 
whether the instrument works correctly. To do this, it is sufficient to 
employ the instrument to measure a known time. If the time chosen be 0, 
the trial consists simply in operating, twice in succession, by means of the 
disjunctor. 
* This operation used to he performed by means of regulating wires of platinum; in the 
instruments of the latest pattern the currents are regulated by means of screw cores in the straight 
electro-magnets of the first and second circuits. 
