Clauson-Thue's public code book cut telegram costs

By the 1870s, international telegraph tariffs charged senders by the word, and a genuine private cipher — letters or figures with no public, independently knowable meaning — was taxed at a punitive rate or restricted outright under international telegraph regulation, aimed at preventing senders from disguising message length or content from telegraph operators and tariff collectors. An ordinary published word, by contrast, was billed at the normal per-word rate regardless of how much information it happened to convey.

Merchants and shippers routinely needed to send long, repetitive business telegrams — shipping terms, cargo tonnage, port of loading, standard commercial phrases — and paying full per-word rates for restating the same boilerplate language on every telegram was a real, recurring cost with no obvious way to shrink it without running afoul of the cipher restrictions.

W. Clauson-Thue published the ABC Universal Commercial Electric Telegraphic Code in 1873, a reference book assigning single code words, drawn from ordinary dictionary vocabulary, to entire pre-drafted business sentences, with blanks the sender filled in for specific figures.

Published a public code book assigning ordinary words to whole sentences, so each word's meaning was publicly knowable and billed normally, despite acting like a cipher.

The tariff taxed private ciphers but not ordinary words, regardless of information content.

Publishing the code book made each code word's meaning publicly knowable, satisfying the legal test.

Operators rarely checked meanings, so the code worked like a private cipher in practice.

The book's wide adoption made the same code words work across many trading partners.

When a rule taxes non-standard units, make your compression publicly documented so it qualifies as standard.

A sender could transmit a single billable code word standing in for what the book's own preface describes as four to upwards of twenty ordinary words of business language, cutting the per-telegram cost of routine commercial messages substantially while remaining on the untaxed side of the code/cipher line.