. Electrical world. ed in the measurement of smallpotentials and in the comparisons for ohmic value of standard resist-ances. Indefinite prolongation of the lower portion of the scale ispossible, enabling thermo-j unction temperature measurements to betaken w-ith greater ease and accuracy. Indefinite prolongation ofthe whole scale is possible with consequently greater range. Thewhole instrument is alive for measurements, with no dead portion,as in the older form of apparatus. The various applications are de-scribed in detail.—Lond. Elec, January 15. Frequency Measurements.—H.^rtmaxn - Kempf.—A
. Electrical world. ed in the measurement of smallpotentials and in the comparisons for ohmic value of standard resist-ances. Indefinite prolongation of the lower portion of the scale ispossible, enabling thermo-j unction temperature measurements to betaken w-ith greater ease and accuracy. Indefinite prolongation ofthe whole scale is possible with consequently greater range. Thewhole instrument is alive for measurements, with no dead portion,as in the older form of apparatus. The various applications are de-scribed in detail.—Lond. Elec, January 15. Frequency Measurements.—H.^rtmaxn - Kempf.—An illustratedarticle in which he gives an account of careful measurements of theexactness of his instruments for measuring frequency. The principleis to subject small pieces of sheet steel or steel tongues (as usedin some musical instruments) to the influence of an electromagnet,which is excited by the current, the frequency of which is to bemeasured. There is provided a series of such steel tongues of differ-. riG. 2.—instrument for measuring frequencies. ent lengths, tuned to different frequencies. The action of the electro-magnet will set that tongue into vibration which is in resonance withthe frequency of the exciting current. The vibrations of the tongue ?RBKLAKV 2~, 1904. ELECTRICAL WORLD and ENGINEER. 409 may be observed either by the eye or by ihe ear. An instrument ofI he latter kind is shown in Fig. 2. He found that the wave form ofihe exciting current or the value of its amplitude did not materiallychange the result. The applications of the instrument to measure-ments of the variation of the frequency to the coimection of alter-iiators in parallel and to the determination of the speed of the prime-mover are discussed.—Elek. Zeit., January 21. REFERENCES. Calibrating Electrometers.—Harms.—While endeavoring to meas-ure the smallest currents through gases in absolute units, he foundthat it was impossible to determine the capacity of electrometerswith suff
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