conducting substances."

Professor Fleeming Jenkin said, "The pressure of the carbons is what
favors the transmission of sound."

All the above named scientific men agree that variations of a current
passing through a carbon microphone are produced by _pressure_ of the
carbons against one another, and they also agree that a jolting motion
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