178 
FESSENDEN. 
however, aluminum is a valuable check to any abnormal 
and unnecessary increase in the price of copper, all present 
danger of which, however, will probably be eliminated by 
the discovery of new methods and deposits, due to the present 
high prices. 
The production of aluminum is increasing at a rapid rate, 
and no difficulty seems to be met with in disposing of it. 
ELECTRICAL INSTRUMENTS. 
Even a brief review of this field is impossible. A few in¬ 
struments, however, may be mentioned. The testing ap¬ 
paratus designed by Mr. Fisher is a marked advance in this 
class of apparatus, and will enable many kinds of testing to 
be completed in but a fraction of the time previously taken. 
The distinctive feature, aside from details of construction, is 
the use of a commutating switch, which makes all the neces¬ 
sary connections for a test by one motion of a handle. 
Methods of winding resistances have been improved, so that 
not only is the self-induction done away with, but also the 
capacity is also rendered negligible—a matter which is of 
great importance where alternating currents are used, and 
which prohibits the use of resistance boxes constructed on 
the old methods. Nichols’ application of the principle of 
the Crooks effect to the construction of a radiometer has at 
last given us an instrument capable of being affected by the 
light from the stars. The universal shunt for galvanometers 
invented by Professor Ayrton is an improvement of the 
greatest value. Work is still being prosecuted on standards 
of resistance and of electromotive force, but as yet the prob¬ 
lem has not been solved with perfect satisfaction, as all the 
low temperature coefficient resistance materials are liable to 
considerable alternations of resistance if the temperature is 
changed much from normal, and the Clarke and Weston 
cells also change their values considerably when subjected 
to abnormal conditions of temperature. The writer has sug¬ 
gested the use of lead wire in a bulb filled with hydrogen 
and containing also a platinum resistance for measuring 
temperature as a permanent standard. 
