106 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
to be described, led us to make experiments with one of Apps’s usual coils for 6-incb 
sparks. 
The diagram (fig. 29) shows the arrangement of the apparatus : A Z, the battery, is 
Eig. 29. 
connected 'permanently with the condenser C, A to one plate, Z to the other ; the A 
terminal of the battery is also connected to one terminal of the primary of the coil, 
the Z terminal to a make-and-break- wheel B, to be worked by hand, thence to the 
key K, which is connected to the other terminal of the coil.* If the key K is pressed 
down, and the wheel B is made to rotate, it is evident that a current will pass, or 
not pass through the primary of the coil, according as a conducting or a non-conducting 
tooth of the break-wheel is in connexion with the contact spring ; but the battery is 
never disconnected from the condenser by the rotation of the break-wheel ; therefore, 
when the make-and-break-wheel permits of the current passing through the primary 
of the coil, it is the accumulated charge of the condenser which actually passes through 
it, and hence produces a very exalted effect in comparison to that of the battery alone. 
Experiments were made with Apps’s 819 coil, already described ; also with — 
Apps’s coil, 815. 
Length of wire. 
Diam. of wire, 
inch. 
Resistance. 
ohms. 
Turns. 
Primary 
78 feet 
0-06 
0-245 
270 
Secondary 
4408 yards 
0-0055 
2196-000 
13,000 
and Apps’s coil, No. 821, for producing 
a 6 -inch spark : 
i — 
Length of wire. 
Diam. of a wire, 
inch. 
Resistance. 
Turns. 
Primary 
66 yards 
0-065 
0-22 
250 
Secondary 
miles 
0-0068 
4900-00 
24,000 
The break-wheel B B and key Tv K' are shown in .position, fig. 9, page 63. 
