Discussion on “induction type indicating instruments” (Macgahan),: “compensating wattmeters” (Ellis),: “hot-wire instruments” (Pierce and Tressler), and “resonant circuit frequency indicator (Pratt and Pric

F. P. Cox: Taking up the paper on hot-wire instruments first, it seems to me that there are limits to the use of this instrument, and yet there are occasions and circumstances where this particular type of instrument is better suited than any other type. For the measurement of low voltages, and particularly for the measurement of circuits of high frequency, I think we must all agree that it has no peer. But beyond those particular fields, it seems to me that its usefulness is rather limited, and limited, indeed, by the very reason that Mr. Pierce mentions, its high energy loss, which, for the 2000 ampere meter mentioned for the voltage given would come to 600 watts, which would be quite out of all reason. I would also mention, not from my personal experience, but a statement that I have very direct from some wireless people, that when you use it on the very high frequencies, it is desirable to use an air transformer rather than a shunt. I cannot give you any figures at all on that, but Mr. Price, who was with Fessenden, at Brant Rock, had very considerable experience with it, and strongly recommended the use of air transformers, in place of shunts, for high frequency.