n
could not be relied upon to reproduce articulate speech.

Mr. Conrad Cooke said, "The first and most striking principle of Hughes'
microphone is a shaking and variable contact between the two parts
constituting the microphone." "The shaking and variable contact is
produced by the movable portion being effected by sound." "Under Hughes'
system, where gas carbon was used, the instruments could not possibly
work upon the principle of pressure." "I am satisfied that it is not
pressure in the sense of producing a change of resistance." "I do not
think pressure has anything to do with it."

Professor Blyth said: "The Hughes microphone depends essentially upon
the looseness or delicacy of contact." "I have heard articulate speech
with such an instrument without a diaphragm." "There is no doubt that to
a certain extent there must be a change in the number of points of
surface contact when the pencil is moved." "The action of the Hughes
microphone depends more or less upon the looseness or delicacy of the
contact and upon the changes in the number of points of surface contact
when the pencil is moved."

Mr. Oliver Heaviside, in _The Electrician_ of 10th February last,
writes: "There should be no jolting or scraping." "Contacts, though
light, should not be loose."

[Illustration: Fig. 2.]

A writer, who signs "W.E.H.," in _The Electrician_ of 24th February
last, says: "The variation of current arises from a variation of
conductivity between the electrodes, consequent upon the variation of
the closeness or pressure of contact;" and also, "there must be a
variation of pressure between the electrodes when the transmitter is in
action."

It seems, then, that some scientific men agree that variation of
pressure is required to produce action in a microphone, and some of them
admit that a microphone with loose contacts will transmit articulate
speech, while others deny it, and some admit that a jolting or shaking
motion of the parts of the microphone does not interfere with articulate
speech, while others say such motion would break the circuit, and cannot
be relied on.

I will now describe two microphones in which there is a shaking or
jolting motion, and loose contacts, and no variation of pressure of the
carbons against one another, and both of these microphones when used
with an induction coil and battery give most excellent articulation. One
of these microphones is made as follows: Two flat plates of carbon are
secured