356 
VELOCITY AND PRESSURE INSTRUMENTS. 
The other end of this lever carries a disc, 0, fixed to a screw, by means of 
which it can be raised or lowered as required. 
This disc is vertically below the registrar when suspended to its electro¬ 
magnet ; consequently, when the current through the second screen is broken, 
the registrar falls on the disc, and releases the spring, H. 
The tube, L (Plate I., Pig. 1), retains the registrar after its fall. 
If it be required to alter the time taken by the registrar to release the knife, 
it is done by raising or lowering the disc of the trigger by turning it in the 
direction with the sun to increase the time, and against the sun to reduce it. 
The screw has a pitch of one millemetre, and the circumference of the disc 
is divided by notches into ten equal parts, in which the paul, P, works. By 
this arrangement the disc can be moved any required number of tenths of a 
millemetre (within certain limits), and is retained in the required position by 
the paul. 
The screw, M, passes through the lever, and acts against the fulcrum sup¬ 
porting it. It is intended for regulating the hold of the catch of the lever on 
the spring, which should always be as light as possible. 
This is regulated once for all; but should the spring at any time show a 
tendency to escape of itself, this defect can be remedied by slightly with¬ 
drawing the screw, M. 
The disjunctor (Plate II., Fig. 9) is composed of a mainspring, t, carrying 
a cross-piece, u , covered with insulating material, and passing under the two 
steel plates, q q'. By pressing the milled-headed screw, £, the spring is com¬ 
pressed and held by the catch, x, allowing the plates, q q[, to come into contact 
with the metal pins, r r', and thus complete the circuits by bringing the screws, 
s v and s'v r , into connexion with one another. When the catch, x , is pressed, 
the mainspring being released, its cross-piece strikes the two plates exactly at 
the same instant, raises them from the screws, and thus breaks both currents 
identically at the same time. 
Should it be thought at any time that the disjunctor is working inaccurately, 
the method of testing it, and of correcting it when out of order, is very simple, 
and will be described under the heading of “ Method of Correcting Irregu¬ 
larities." 
The arrangement of the screens and electric current is precisely the same as 
when using the Navez-Leurs instrument, except that the chronometer battery 
must be increased in strength (because its electro-magnet is required to 
support a greater weight than in the Navez-Leurs instrument), and a dif¬ 
ferent method must be adopted for introducing the disjunctor into the circuit 
(Plate III.) With the Le Boulenge chronograph, the two wires from the 
positive poles of the batteries are not joined as with the Navez-Leurs, 
but are taken to the two connecting screws, s s', of the disjunctor; and thus 
the two currents, though passing through the disjunctor, are kept entirely 
separate. (Plate III.) 
The electro-magnet, A, is magnetised by the current passing through the 
first screen; consequently, when the shot cuts this screen the chronometer is 
released and falls freely in a vertical direction. 
The other electro-magnet is in the circuit through the second screen, so that 
the registrar falls when this screen is cut, and, striking the disc on the free 
end of the lever of the trigger, liberates the spring, which carries forward the 
knife until it strikes the chronometer in its fall and makes an indent in the 
upper zinc tube. 
