Sir William Thomson, in the same case, said:  “The function of the carbon is to give rise to diminished resistance by pressure; it possesses the quality of, under slight degrees of pressure, decreasing the resistance to the passage of the electric current;” and, also, “the jolting motion would be a make-and-break, and the articulate sounds would be impaired.  There can be no virtue in a speaking telephone having a jolting motion.”  “Delicacy of contact is a virtue; looseness of contact is a vice.”  “Looseness of contact is a great virtue in Hughes’ microphone;” and “the elements which work advantages in Hughes’ are detrimental to the good working of the articulating instrument.”

[Illustration:  Fig. 1.]

Mr. Falconer King said:  “There would be no advantage in having a jolting motion; the jolting motion would break the circuit and be a defect in the speaking telephone,” and “you must have pressure and partially 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 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.”