By means of
an ammeter and voltmeter used conjointly, the resistance of part of the
circuit, say a lamp or heated wire, can be got by Ohm's law. Profs.
Ayrton and Perry's non-sparking key is designed to prevent sparking with
large currents. It acts by introducing a series of resistance coils
determined experimentally one after the other in circuit, thereby
cutting off the spark.
* * * * *
NEW INSTRUMENTS FOR MEASURING ELECTRIC CURRENTS AND ELECTRO-MOTIVE
FORCE.
By Messrs. R. E. CROMPTON and GISBERT KAPP.
[Footnote: Paper read before the Society of Telegraph Engineers, 14th
February, 1884.]
In consequence of the rapid development of that part of electrical
science which may be termed "heavy electrical engineering," reliable
measuring instruments specially suitable for the large currents
employed in lighting and transmission of energy have become an absolute
necessity. As usual, demand has stimulated supply, and many ingenious
and useful instruments have been invented, the manufacture of which
forms at the present day an important industry.
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