tes Patent Office a large number of contested cases, called
"Interferences," where applications for patents covering the invention
of a similar device have been independently filed by two or even more
persons. In such cases only one patent can be issued, and that to
the inventor who on the taking of testimony shows priority in date of
invention. [20]

[Footnote 20: A most remarkable instance of contemporaneous
invention and without a parallel in the annals of the United
States Patent Office, occurred when, on the same day,
February 15, 1876, two separate descriptions were filed in
that office, one a complete application and the other a
caveat, but each covering an invention for "transmitting
vocal sounds telegraphically." The application was made by
Alexander Graham Bell, of Salem, Massachusetts, and the
caveat by Elisha Gray, of Chicago, Illinois. On examination
of the two papers it was found that both of them covered
practically the same ground, hence, as only one patent could
be granted, it became necessary to ascertain the precise
hour at which the documents were respectively filed, and put
the parties in interference. This was done, with the result
that the patent was ultimately awarded to Bell.]

In the opening up and development of any new art based upon a
fundamental discovery or invention, there ensues naturally an era of
supplemental or collateral inventive activity--the legitimate outcome
of the basic original ideas. Part of this development may be due to
the inventive skill and knowledge of the original inventor and his
associates, who, by reason of prior investigation, would be in better
position to follow up the art in its earliest details than others,
who might be regarded as mere outsiders. Thus a new enterprise may be
presented before the world by its promoters in the belief that they are
strongly fortified by patent rights which will protect them in a degree
commensurate with the risks they have assumed.

Supplemental inventions, however, in any art, new or old, are not
limited to those which emanate from the original workers, for the
ingenuity of man, influenced by the spirit of the times, seizes upon any
novel line of action and seeks to improve or enlarge upon it, or, at
any rate, to produce more or less variation of its phases. Consequently,
there is a constant endeavor on the part of a countless host of men
possessing s