In the latter case the result is remarkably good, but the
apparatus is not free from a certain amount of complication, and
demands, moreover, particular care in its construction, experience
having shown that the induction coils must not be equal, but that they
must present resistances combined according to the circuit doing duty.
It should be added that researches have been continued as to the
bodies proper to be employed as microphonic contact, with the result
of bringing out the important fact that the number of substances that
can be put to this use is almost unlimited. The contacts of the Herz
apparatus are now being made of conducting bodies (metals for example)
reduced to powder and conglomerated by chemical means with a sort of
non-conductive cement. The proportion of the elements depends upon the
conductivity of the materials employed, and it alone determines the
microphonic value of the compound, the nature of the elements
apparently having scarcely any influence.
Nor has the speaking condenser been neglected. As regards this,
efforts have seemingly been made toward finding a convenient
arrangement and a regular mode of construction, the good working of
these apparatus being absolutely dependent upon the care with which
they are set up.
In Dr. Herz's opinion, the telephone is not to remain a single
apparatus, varied only as to form, but, on the contrary, must be
actually modified according to the purposes for which it is designed.
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