728 Hiley. — On the Value of Different Degrees of 
hook K, to which it is fixed. Now as the clock pulley rotates, the twine is 
gradually set free and the weight W slowly falls, keeping the twine tight, 
and while this is proceeding the pulley D is made to rotate, and the arms 
A x , A 2 , A 3 , A±, which are attached to it, pass successively into the mercury 
bath M. The pulley on the clock rotates once an hour, and the arms A x , 
A 2 , A 3 , A± can be made to rotate once in 10 min., 15 min., 40 min., or 
do min., according as the twine is passed round the smaller or larger pulleys 
at D. There being four arms, A x , A 2 , A 3 , A±, one, two, or all of which can 
be used, contacts with the mercury can be regularly made at intervals 
varying from 2^ min. to 60 min. (See also Fig. 5, PI. LVIII.) 
At F is a 2-volt electric accumulator, one terminal of which is con- 
nected with the mercury bath M. To the other terminal is attached a wire 
which passes round the electro-magnet E, and thence is connected with the 
axis of the pulleys at D and the arms A Xi A 2 , A 3 , A±. Thus, when one of 
the arms A Xi A 2i A 3) A± is dipping into the mercury bath M, the current is 
made which makes the electro -magnet operative. 
At the point B is loosely hinged a stiff wire d x d 2 , bent downwards at 
each end. On this wire, in the part Bd X) is fixed a soft iron plate /, just 
above the magnet. The end d 2 is weighted so as to make this end heavier. 
Now when the electro-magnet is not active, the end d 2 , being heavier, 
