158 
MINUTES OE PROCEEDINGS OE 
The operator puts the disjunctor on cock, raises the pendulum with his 
forefinger to the electro-magnet, which retains it; the zero of the vernier 
coincides then with the zero on the limb. The operator then presents the 
weight to the electro-magnet of the conjunctor, which retains it; sometimes 
the weight oscillates round the point of suspension, the operator waits till 
these oscillations cease; then, pressing the trigger of the disjunctor, the 
ivory buffer strikes the springs, breaks both circuits together, and instanta¬ 
neously demagnetizes both magnets at the same moment; the pendulum is 
set in motion, the weight falls, meets the steel blade, presses the pin into the 
mercury, completes the third circuit and instantly magnetizes the large 
electro-magnet, which clamps the washer and needle. 
The operator then removes the weight from the blade, notes the angle 
marked by the needle, detaches the latter from the magnet, and proceeds to 
operate again with the instrument exactly in the same manner. The needle 
again marks an angle, which ought to be the same as that of the first 
operation; if there is a difference, it indicates the degree of regularity in the 
working of the apparatus. A practised experimenter may easily succeed in 
bringing the difference, between two successive operations, to a maximum 
of 0°*25; and he is able to see immediately where the error lies, and knows 
at once the necessary corrections. The angle which the needle marks denotes 
the time, occupied by the leaden weight in falling from its point of suspension 
to the steel blade. 
j 'Employment of the Apparatus. 
15. As soon as the operator is certain that the instrument works regu¬ 
larly, experiments may be proceeded with. The operator must bear in 
mind that the two operations, viz. that performed by means of the disjunctor, 
and that which takes place by the effect of the shot, must be made under 
identical circumstances. Suppose the instrument ready, the targets in their 
places, and the gun charged. The experimenter operates by means of the 
disjunctor, and reads off an angle which we will call A, Fig. 7; then having 
again put the disjunctor on 
cock, and placed the pendulum 
and weight in their initial 
positions, he gives the signal 
to fire. The gun is fired; 
the projectile passes through 
the first target, breaks the 
first circuit, and demagnetizes 
the straight electro-magnet of 
the pendulum; the pendulum, 
in consequence, is set in motion. The projectile then passes through the 
second target, breaks the second circuit, and demagnetizes the conjunctor 
electro-magnet; the weight falls, presses the pin into the mercury, completes 
the third circuit by which the large electro-magnet is made active, and the 
needle clamped. The operator reads the angle, which we will call A', and 
which is larger than A, for this reason, that instead of both currents being 
broken simultaneously, as is the case when operating with the disjunctor, 
they are now broken successively, as there is a certain distance between the 
