4C and 4A--down the center of the cylinder to a divided
contact, into which a switch arm can be shot. When this is so, a
connection is made to the upright brass rod, T, which serves to grip
the band, R, passing round the body of the cylinder. The current then
passes through all the turns of wire above the band, and out at the
other terminal. The resistance can be varied by raising or lowering
the band. Fig. 4B shows the manner of tightening the band against the
wires on the cylinder. The upright rod, T, is seen in section, and is
fixed in one position to the frame of the apparatus. Abutting against
this, and working in the block to which the two ends of the band are
screwed, is a thumb screw, S, by turning which the band may be
loosened for adjusting, and tightened when the right position is
found. The cylinder is covered with asbestos sheet, and the wire,
which is of nickel, and measures altogether from 3 to 4 ohms, is wound
helically round this. The switch arm, to which the handle is attached
below, does not itself make and break the circuit, but carries a
spring, as shown, which, when the arm is at the end of its movement,
pulls over the contact lever with a rapid action, shooting the same
between the divided contact piece, and making a perfect contact. The
switchboard forms one side of a closed wooden case or cupboard, with
sufficient room for a man to enter and adjust the resistances or
switches for each lamp.
Pages:
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75