Note 21 — Chapter IV · CONTEMPORARY DOCUMENTS.

[The so-called “galvanic tone” heard on opening or closing the circuit was well-known, and Wertheim had shown that this tone was, for any given rod of iron, identical with its “longitudinal tone,” i.e. the tone produced by striking it on the end so as to produce longitudinal vibrations. But it was one of the most important discoveries in Reis’s researches that such a rod could take up any tone in obedience to the vibrations forced upon it by periodic interruptions in the magnetising current in the spiral of any degree of rapidity within very wide limits. The translator has had occasion to examine this point, and has found iron, steel, and cobalt wires varying from 4 to 10 inches in length, including some used by Reis himself as receivers, to be capable of taking up vibrations from as slow as 40 per second to the very shrillest whistle audible to human ears, or exceeding 36,000 per second. It is sometimes also mistakenly supposed that such a wire can respond only to the vibrations of tones that are musical, not to those that are articulate, including both consonants and vowels. This, however, is an entire mistake. For, using such a wire as a receiver (surrounded by its proper coil and mounted with an appropriate sounding board, or, better still, tympanum), in conjunction with a well-adjusted transmitter, the articulation transmitted surpasses that obtainable with any of the ordinary magnetic receivers in distinctness, though not in loudness. This discovery of Reis’s is of the greatest importance, especially as some who ought to know better have very unjustly denied the capability of this part of the apparatus to act as a telephone receiver for articulate sounds.]—S. P. T.