The Information - James Gleick [76]
For Wilkins the issues of cryptography stood near the fundamental problem of communication. He considered writing and secret writing as essentially the same. Leaving secrecy aside, he expressed the problem this way: “How a Man may with the greatest Swiftness and Speed, discover his Intentions to one that is far distant from him.”♦ By swiftness and speed he meant, in 1641, something philosophical; the birth of Isaac Newton was a year away. “There is nothing (we say) so swift as Thought,” he noted. Next to thought, the swiftest action seemed to be that of sight. As a clergyman, he observed that the swiftest motion of all must belong to angels and spirits. If only a man could send an angel on an errand, he could dispatch business at any distance. The rest of us, stuck with Organical Bodies, “cannot communicate their Thoughts so easie and immediate a way.” No wonder, Wilkins wrote, that angels are called messengers.
As a mathematician, he considered the problem from another side. He set out to determine how a restricted set of symbols—perhaps just two, three, or five—might be made to stand for a whole alphabet. They would have to be used in combination. For example, a set of five symbols—a, b, c, d, e—used in pairs could replace an alphabet of twenty-five letters:
“According to which,” wrote Wilkins, “these words, I am betrayed, may be thus described: Bd aacb abaedddbaaecaead.” So even a small symbol set could be arranged to express any message at all. However, with a small symbol set, a given message requires a longer string of characters—“more Labour and Time,” he wrote. Wilkins did not explain that 25 = 52, nor that three symbols taken in threes (aaa, aab, aac,…) produce twenty-seven possibilities because 33 = 27. But he clearly understood the underlying mathematics. His last example was a binary code, awkward though this was to express in words:
Two Letters of the Alphabet being transposed through five Places, will yield thirty two Differences, and so will more than serve for the Four and twenty Letters; unto which they may be thus applied.
Two symbols. In groups of five. “Yield thirty two Differences.”
That word, differences, must have struck Wilkins’s readers (few though they were) as an odd choice. But it was deliberate and pregnant with meaning. Wilkins was reaching for a conception of information in its purest, most general form. Writing was only a special case: “For in the general we must note, That whatever is capable of a competent Difference, perceptible to any Sense, may be a sufficient Means whereby to express the Cogitations.”♦ A difference could be “two Bells of different Notes”; or “any Object of Sight, whether Flame, Smoak, &c.”; or trumpets, cannons, or drums. Any difference meant a binary choice. Any binary choice began the expressing of cogitations. Here, in this arcane and anonymous treatise of 1641, the essential idea of information theory poked to the surface of human thought, saw its shadow, and disappeared again for four hundred years.
The contribution of the dilettantes is what the historian of cryptography David Kahn calls the excited era triggered by the advent of the telegraph.♦ A new public interest in ciphers arose just as the subject bloomed in certain intellectual circles. Ancient methods of secret writing appealed to an odd assortment of people, puzzle makers