Because of Samuel White's opposition to Gray working on the telephone, Gray did not tell anybody about his invention for transmitting voice sounds until February 11, 1876 (Friday). Gray requested that his patent lawyer William D. Baldwin prepare a "caveat" for filing at the US Patent Office. A "caveat was like a provisional patent application with drawings and description but without a request for examination.
On Monday morning February 14, 1876, Gray signed and had notarized the caveat that described a telephone that used a liquid transmitter. Baldwin then submitted the caveat to the US Patent Office. That same morning a lawyer for "Alexander Graham Bell submitted Bell's patent application. Which application arrived first is hotly disputed, although Gray believed that his caveat arrived a few hours before Bell's application. Bell's lawyers in Washington, DC, had been waiting with Bell's patent application for months, under instructions not to file it in the USA until it had been filed in Britain first. (At the time, Britain would only issue patents on discoveries not previously patented elsewhere.)
According to Evenson, during the weekend of February 12–14, 1876, before either caveat or application had been filed in the patent office, Bell's lawyer learned about the liquid transmitter idea in Gray's caveat that would be filed early Monday morning February 14. Bell's lawyer then added seven sentences describing the liquid transmitter and a variable resistance claim to Bell's draft application. After the lawyer's clerk recopied the draft as a finished patent application, Bell's lawyer hand-delivered the finished application to the patent office just before noon Monday, a few hours after Gray's caveat was delivered by Gray's lawyer. Bell's lawyer requested that Bell's application be immediately recorded and hand-delivered to the examiner on Monday so that later Bell could claim it had arrived first. Bell was in Boston at this time and was not aware that his application had been filed.
Five days later, on February 19, Zenas Fisk Wilber, the patent examiner for both Bell's application and Gray's caveat, noticed that Bell's application claimed the same variable resistance feature described in Gray's caveat. Wilber suspended Bell's application for 90 days to give Gray time to submit a competing patent application. The suspension also gave Bell time to amend his claims to avoid an interference with an earlier patent application of Gray's that mentioned changing the intensity of the electric current without breaking the circuit, which seemed to the examiner to be an "undulatory current" that Bell was claiming. Such an interference would delay Bell's application until Bell submitted proof, under the "first to invent rules, that Bell had invented that feature before Gray.
Bell's lawyer telegraphed Bell, who was still in Boston, to come to Washington, DC. When Bell arrived on February 26, Bell visited his lawyers and then visited examiner Wilber who told Bell that Gray's caveat showed a liquid transmitter and asked Bell for proof that the liquid transmitter idea (described in Bell's patent application as using mercury as the liquid) was invented by Bell. Bell pointed to an application of Bell's filed a year earlier where mercury was used in a circuit breaker. The examiner accepted this argument, although mercury would not have worked in a telephone transmitter. On February 29, Bell's lawyer submitted an amendment to Bell's claims that distinguished them from Gray's caveat and Gray's earlier application. On March 3, Wilber approved Bell's application and on March 7, 1876, U.S. Patent 174,465 was published by the "U.S. Patent Office.
Bell returned to Boston and resumed work on March 9, drawing a diagram in his lab notebook of a water transmitter being used face down, very similar to that shown in Gray's caveat. Bell and Watson built and tested a liquid transmitter design on March 10 and successfully transmitted clear speech saying "Mr. Watson – come here – I want to see you." Bell's notebooks became public when they were donated to the Library of Congress in 1976.
Although Bell has been accused of stealing the telephone from Gray because his liquid transmitter design resembled Gray's, documents in the Library of Congress indicate that Bell had been using liquid transmitters extensively for three years in his multiple telegraph and other experiments. In April, 1875, ten months before the alleged theft of Gray's design, the U.S. Patent Office granted U.S. Patent 161,739 to Bell for a primitive fax machine, which he called the "autograph telegraph." The "patent drawing includes liquid transmitters.
After March 1876, Bell and Watson focused on improving the electromagnetic telephone and never used Gray's liquid transmitter in public demonstrations or commercial use. When Bell demonstrated his telephone at the Centennial Exhibition in June 1876, he used his improved electromagnetic transmitter, not Gray's water transmitter.
Although Gray had abandoned his caveat, Gray applied for a patent for the same invention in late 1877. This put him in a second interference with Bell's patents. The "Patent Office determined, "while Gray was undoubtedly the first to conceive of and disclose the [variable resistance] invention, as in his caveat of February 14, 1876, his failure to take any action amounting to completion until others had demonstrated the utility of the invention deprives him of the right to have it considered." Gray challenged Bell's patent anyway, and after two years of litigation, Bell was awarded rights to the invention, and as a result, Bell is credited as the inventor.
In 1886, Wilber stated in an "affidavit that he was an alcoholic and deeply in debt to Bell's lawyer "Marcellus Bailey with whom Wilber had served in the Civil War. Wilber stated that, contrary to Patent Office rules, he showed Bailey the caveat Gray had filed. He also stated that he showed the caveat to Bell and Bell gave him $100. Bell testified that they only discussed the patent in general terms, although in a letter to Gray, Bell admitted that he learned some of the technical details. Wilbur's affidavit contradicted his earlier testimony, and historians have pointed out that his last affidavit was drafted for him by the attorneys for the Pan-Electric Company which was attempting to steal the Bell patents and was later discovered to have bribed the U.S. Attorney General "Augustus Garland and several Congressmen.
Bell's patent was disputed in 1888 by attorney Lysander Hill who accused Wilber of allowing Bell or his lawyer Pollok to add a handwritten margin note of seven sentences to Bell's application that describe an alternate design similar to Gray's liquid microphone design. However, the marginal note was added only to Bell's earlier draft, not to his patent application that shows the seven sentences already present in a paragraph. Bell testified that he added those seven sentences in the margin of an earlier draft of his application "almost at the last moment before sending it off to Washington" to his lawyers. Bell or his lawyer could not have added the seven sentences to the application after it was filed in the Patent Office, because then the application would not have been suspended.
In 1887 Gray invented the "telautograph, a device that could remotely transmit handwriting through telegraph systems. Gray was granted several patents for these pioneer fax machines, and the Gray National Telautograph Company was chartered in 1888 and continued in business as The Telautograph Corporation for many years; after a series of mergers it was finally absorbed by "Xerox in the 1990s. Gray's telautograph machines were used by banks for signing documents at a distance and by the military for sending written commands during gun tests when the deafening noise from the guns made spoken orders on the telephone impractical. The machines were also used at train stations for schedule changes.["citation needed]
Gray displayed his telautograph invention in 1893 at the "1893 Columbian Exposition and sold his share in the telautograph shortly after that. Gray was also chairman of the International Congress of Electricians at the World's Columbian Exposition of 1893.
Gray conceived of a primitive "closed-circuit television system that he called the "telephote". Pictures would be focused on an array of selenium cells and signals from the selenium cells would be transmitted to a distant station on separate wires. At the receiving end each wire would open or close a shutter to recreate the image.
In 1899 Gray moved to Boston where he continued inventing. One of his projects was to develop an underwater signaling device to transmit messages to ships. One such signaling device was tested on December 31, 1900. Three weeks later, on January 21, 1901, Gray died from a heart attack in "Newtonville, Massachusetts.
Gray wrote several books including:
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