ABSTRACTS 



Authors of scientific papers are requested to see that abstracts, preferably 

 prepared and signed by themselves, are forwarded promptly to the editors. 

 The abstracts should conform in length and general style to those appearing in 

 this issue. 



APPARATUS. — A new form of vibration galvanometer. P. G. Agnew. 

 Bur. Standards Sci. Paper 370. Pp. 8 (37-44). 1920. 



Vibration galvanometers are very useful in a. c. null measurements, 

 but have not been much used in industrial laboratories on account of 

 their being sensitive to external vibrations and requiring delicate ad- 

 justments. The present instrument, which has a sensitivity higher 

 than other forms of the moving-iron type, but less than that of the 

 most sensitive forms of the moving-coil type, has the advantages of 

 sturdiness, quick responsiveness, and freedom from the effects of ex- 

 ternal vibration. It consists essentially of a fine steel wire mounted 

 on one pole of a permanent magnet and so arranged that the free end 

 of the wire may vibrate between the poles of an electromagnet through 

 which flows the current to be detected. The motion of the wire is 

 observed with a microscope. 



The "resonance range" is about one per cent; that is, if the frequency 

 of the current is one per cent, above or below the frequency of reso- 

 nance, the amplitude of vibration will be half as great as at resonance. 

 The sensitivity is such that with a i-ohm winding an e. m. f. of 3 micro- 

 volts may be detected, and with a 270-ohm winding a current of 0.05 

 microampere can readily be detected. P. G. A. 



ELECTRICAL ENGINEERING.— Lra/^ag^ resistance of street rail- 

 way roadbeds and its relation to electrolysis of underground struc- 

 tures. E. R. Shepard. Bur. Standards Tech. Paper 127. Pp. 

 39, pi. I, figs. 9. 1919. 



Electrolytic damage to underground piping systems is caused by 

 the escape of current from the rails of electric lines and the resistance 

 of the roadbed is an important factor in the amount of current which 

 may escape. 



Short sections of fourteen common types of roadbeds were constructed 

 on the grounds of the Bureau of Standards and resistance measure- 

 ments under varying weather conditions were carried on for a period 

 of three years. Some measurements were also made on a number of 

 city lines in and about Washington, both open track and several types 



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