Discussion on “some fundamental characteristics of mercury vapor apparatus,” at Milwaukee, Wis., May 30, 1906

C. P. Steinmetz: As stated in the concluding sentence, this paper is not confined to new matter, it is also somewhat historical in that it reviews in part much of the work that has been done with mercury arc apparatus. As regards the statement of facts contained in the paper, in general I agree with the author; but with his interpretations and explanations of facts I must disagree to a considerable extent, partly for the reason that the paper describes as features of a special class of phenomena features which are characteristic of a far more general class of phenomena; that is, characteristics of arcs in general, the common carbon arc, well known to us for a century, as well as the mercury arc. Furthermore, well-known features are re-explained in connection with the mercury arc by the introduction of new terms; for instance, the so-called cathode or negative resistance, which is nothing more than a reiteration of the fact that an electric arc does not start itself, but must be started. That was known a century ago by Davy, when he drew the first powerful arc by putting battery terminals together and then separating them. But Davy did not introduce the term “negative resistance,” he merely stated the phenomena, which since that time has been used by every designer and operator of arc lamps, though I do not think many of the designers and operators have ever heard anything about negative resistance.