Mathiessen and others have since enunciated
the law according to which this rise of resistance varies with rise of
temperature; and Siemens has further perfected his apparatus, and
applied it as a pyrometer to the measurement of furnace fires. It forms
in reality an electric thermometer, which will indicate the temperature
of an inaccessible spot. A coil of platinum or platinum-alloy wire is
enclosed in a suitable fire-proof case and put into the furnace of which
the temperature is wanted. Connecting wires, properly protected, lend
from the coil to a differential voltameter, so that, by means of the
current from a battery circulating in the system, the electric
resistance of the coil in the furnace can be determined at any moment.
Since this resistance depends on the temperature of the furnace, the
temperature call be found from the resistance observed. The instrument
formed the subject of the Bakerian lecture for the year 1871.
Siemens's researches on this subject, as published in the JOURNAL OF
THE SOCIETY OF TELEGRAPH ENGINEERS (Vol. I., p. 123, and Vol. III., p.
297), included a set of curves graphically representing the relation
between temperature and electrical resistance in the case of various
metals.
The electric pyrometer, which is perhaps the most elegant and
original of all William Siemens's inventions, is also the link which
connects his electrical with his metallurgical researches.
Pages:
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161