The
same salt may be used to caseharden wrought iron.
* * * * *
APPARATUS FOR MEASURING SMALL RESISTANCES.
The accompanying engraving shows a form of Thomson's double bridge, as
modified by Kirchhoff and Hausemann. The chief advantage claimed for
this instrument consists in the fact that all resistances of defective
contact between the piece to be measured and the battery are entirely
eliminated--an object of prime importance in measuring very small
resistances. By the use of this instrument resistances can be measured
accurately down to one-millionth of a Siemens unit.
The general arrangement of the instrument is shown in Fig. 1; Fig. 2
being a diagram of the electrical connections.
[Illustration: FIG. 1.--KIRCHHOFF AND HANSEMANN'S BRIDGE FOR MEASURING
SMALL RESISTANCES.]
The piece of metal to be measured, M, is placed in the measuring forks,
gg, in such a manner that the movable fork is removed as far as possible
from the stationary one; if the weight of the piece be insufficient to
secure a good connection, additional weights may be placed upon it.
Pages:
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85