82 abstracts: electricity 



ELECTRICITY. — A device for measuring the torque of electrical instru- 

 ments. P. G. Agnew. Bulletin Bureau of Standards, 7: 45-48. 

 1911. 



The device consists essentially of a dynamometer of the pendulum 

 type. A needle is attached to the bob of the pendulum to serve as a 

 pointer which swings closely over a scale consisting of 153 concentric 

 circles engraved on the concave surface of a very shallow spherical bowl 

 of a radius of curvature of one meter. The bob is suspended by a silk 

 fiber at the center of curvature of this scale, which reads tangents of 

 angles directly, the divisions being approximately 1 mm. and hence 

 indicating angles whose tangents are 0.001, 0.002, etc. The force to be 

 measured (always horizontal) is transmitted to the bob by a second 

 fiber attached at its center of mass. The force in grams is then equal 

 to the product of the weight of the bob into the number of divisions 

 deflection. The range may be changed by attaching extra weights to 

 the bob. 



In measuiing the torque of a deflection instrument — for example a 

 voltmeter— the horizontal thread is fastened to the pointer at a con- 

 venient distance from the pivot and the voltmeter moved horizontally 

 until the desired deflection is produced. We then have 



Torque = arm X weight X 0.001 X reading in divisions. 



In the case of a watthour meter it is necessary only to attach the 

 thread to the edge of the disk, apply current and voltage to the meter, 

 and allow the thread to wind upon the disk as far as it will. Under 

 proper conditions an accuracy of 0.1 per cent may be obtained. The 

 torques of some types of instruments have been found to range as 

 follows: D. C. voltmeter 0.3 to 2.1 gram-cm.; D. C. ammeters 0.2 to 

 0.9 gram-cm.; A. C. watthour meters 3.0 to 7.8 gram-cm. P. G. A. 



RADIO-TELEGRAPHY. — Quantitative experiments in long distance 

 radio-telegraphy. L. W. Austin, U. S. Naval Wireless Tele" 

 graphic Laboratory. Bulletin Bureau of Standards, 7: 315-363. 

 1911. 



The U. S. naval wireless laboratory during the winter 1909-1910 and 

 the spring and summer of 1910 carried on quantitative measurements 

 on the relation between the currents in the sending and receiving radio- 

 telegraphic antennas. This work was taken up in connection with the 

 testing of the wireless set at the Brant Rock station and those of the 

 scout cruisers Birmingham and Salem. The Brant Rock station devel- 



