Here Bi is the reading of the B arm resistance box with Cn disconnected, B2 its reading with the standard set at a value of Cjv-

With this arrangement an initial balance was established against a Q of 20 (known to about =tl%, from resonance bridge measurements). The Q's of several other coils were then measured, the results checking the known values within essentially the accuracy of reading of the condenser Ca- Additional correction terms are introduced into the inductance equation by the transformer capacitance shunting the series inductance Lia- For the case cited, this correction is negligible, but it can become significant if large inductances are used in the A arm. — Ivan G. Easton aThe resistance of the choke must, of course, be added to Ra. The choke resistance is small compared to Ra, however, and the d-c value may be used without introducing any appreciable error.


We regret that, owing to circumstances beyond our control, we can no longer supply vacuum thermocouples. Consequently, all models of Type 493 Thermocouples are discontinued, effective December 1.

using the cathode-ray oscillograph in frequency comparisons

•IN FREQUENCY MEASUREMENT AND CALIBRATION, where an unknown frequency is to be compared with, or adjusted to, a standard frequency, the cathode-ray oscillograph offers a convenient and precise means of making the necessary comparison. The following summary of the various ways in which a cathode-ray oscillograph can be used advantageously in frequency measurement presents no new methods. The methods discussed are presented particularly for those who may have available a cathode-ray oscillograph, but who may not appreciate its potentialities in this field.

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