The Invention of the Telephone

Exhibit 2: Gray's Caveat

Elisha Gray's caveat, as it was filed in the United States Patent Office, February 14, 1876

To all whom it may concern: Be it known that I, Elisha Gray, of Chicago, in the County of Cook, and State of Illinois, have invented a new art of transmitting vocal sounds telegraphically, of which the following is a specification:

It is the object of my invention to transmit the tones of the human voice through a telegraphic circuit, and reproduce them at the receiving end of the line, so that actual conversations can be carried on by persons at long distances apart.

I have invented and patented methods of transmitting musical impressions or sounds telegraphically, and my present invention is based upon a modification of the principle of said invention, which is set forth and described in letters patent of the Unit ed States, granted to me July 27th, 1875, respectively numbered 166,095, and 166,096, and also in an application for letters patent of the United States, filed by me, February 23d, 1875.

To attain the objects of my invention, I devised an instrument capable of vibrating responsively to all tones of the human voice, and by which they are rendered audible.

In the accompanying drawings I have shown an apparatus embodying my improvements in the best way now known to me, but I contemplate various other applications, and also changes in the details of construction of the apparatus, some of which would obviou sly suggest themselves to a skillful electrician, or a person in the science of acoustics, in seeing this application.

Fig. 1 represents a vertical central section through the transmitting instrument; Fig. 2, a similar section through the receiver; and Fig. 3,a diagram representing the whole apparatus.

My present belief is, that the most effective method of providing an apparatus capable of responding to the various tones of the human voice, is a tympanum, drum or diaphragm, stretched across one end of the chamber, carrying an apparatus for producing fluctuations in the potential of the electric current, and consequently varying in its power.

In the drawings, the person transmitting sounds is shown as talking into a box, or chamber, A, across the outer end of which is stretched a diaphragm, a, of some thin substance, such as parchment or gold-beaters' skin, capable of responding to all the vibrations of the human voice, whether simple or complex. Attached to this diaphragm is a light metal rod, A', or other suitable conductor of electricity, which extends into a vessel B, made of glass or other insulating material, having its lower end clo sed by a plug, which may be of metal, or through which passes a conductor b, forming part of the circuit.

This vessel is filled with some liquid possessing high resistance, such, for instance, as water, so that the vibrations of the plunger or rod A', which does not quite touch the conductor b, will cause variations in resistance, and, consequently, in the potential of the current passing through the rod A'.

Owing to this construction, the resistance varies constantly in response to the vibrations of the diaphragm, which, although irregular, not only in their amplitude, but in rapidity, are nevertheless transmitted, and can, consequently, be transmitted through a single rod, which could not be done with a positive make and break of the circuit employed, or where contact points are used.

I contemplate, however, the use of a series of diaphragm in a common vocalizing chamber, each diaphragm carrying and independent rod, and responding to a vibration of different rapidity and intensity, in which case contact points mounted on other diaphragms may be employed.

The vibrations thus imparted are transmitted through an electric circuit to the receiving station, in which circuit is included an electro-magnet of ordinary construction, acting upon a diaphragm to which is attached a piece of soft iron, and which dia phragm is stretched across a receiving vocalizing chamber c, somewhat similar to the corresponding vocalizing chamber A.

The diaphragm at the receiving end of the line is this thrown into vibration corresponding with those at the transmitting end, and audible sounds or words are produced.

The obvious practical application of my improvement will be to enable persons at a distance to converse with each other through a telegraphic circuit, just as they do now in each other's presence, or through a speaking tube.

I claim as my invention the art of transmitting vocal sounds or conversations telegraphically through an electric circuit.

Elisha Gray.

Witnesses: William J. Peyton, Wm. D. Baldwin.

For Gray's original notebook entry which led to his caveat, click here

[ Back to Top ]

[ Previous Exhibit ] [ Next Exhibit ]

[ Syllabus ] [ Exhibits Home ]

Unless otherwise noted this page and all its contents and subdocuments are copyright 1994 by Michael E. Gorman.

This page was last edited: Sunday, July 18, 1999