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ANY reader of detective stories knows to watch for subtle anomalies. A dozen years ago I spotted one while investigating the history of fibre optics. In an interview in 1921, less than a year before his death, Alexander Graham Bell had said that he considered his greatest invention to be the , an obscure device that modulated the intensity of reflected sunlight to transmit voices through the open air. The choice struck me as odd, but I didn’t investigate it further.

spotted another anomaly when studying Bell’s notebook from the time of his 1876 telephone experiments. of his voice transmitter was strikingly similar to a drawing had included in a patent filing made at almost the same time as Bell’s lawyer filed his telephone patent. Clearly a better detective than I am, Shulman dug into historical archives.

The standard version of Bell’s oft-told tale is that he succeeded because his lawyer reached the US Patent Office just hours before Gray. Yet when Shulman checked patent office records for 1876, he found they recorded only the day of filing, not the time. Moreover, Bell’s notebook sketch of the transmitter was dated just after he had returned to Boston from a trip to the Washington patent office to sort out his application.

Could Bell have seen Gray’s supposedly secret filing? Shulman builds a compelling case: Bell avoided discussing the details of his telephone transmitter until he could talk about a later version which bore less resemblance to Gray’s; the transmitter design details were inserted on the edge of his handwritten patent filing; the patent office’s handling of the case was unusual; and Bell was under intense pressure from his financial backer and soon-to-be father-in-law, Gardiner Hubbard.

Shulman caps his list by tracking down a statement by a patent examiner who claimed to have shown Gray’s filing to Bell. It’s nearly a smoking gun, but the examiner was an alcoholic who had given several other accounts.

Bell’s notebooks were never entered as evidence in the series of lawsuits over his patent, and were not opened to scholars until 1976. He couldn’t avoid testifying in the suits, but he distanced himself from the business side of things. When he proffered the photophone as his greatest invention, was it because it was his original work alone? Read the book and decide – it’s a great tale of historic detection.