abstracts: electricity, geology 389 



ELECTRICITY. — The testing of instrument transformers. P. G. Agnew 

 and F. B. Silsbee. Proceedings American Institute Electrical 

 Engineers. June, p. 1267. 1912. 



This paper describes a new arrangement for testing instrument trans- 

 formers, which has recently been developed at the Bureau of Standards. 

 For current transformers the ratio is found as formerly by balancing 

 the IR drops in two resistances, but the phase angle is measured by using 

 the secondary voltage of a mutual inductance to balance the quadra- 

 ture component of the voltage drops. A vibration galvanometer is 

 used as a detector, and when a complete balance is obtained both ratio 

 and phase angle can be computed from the values of the resistances and 

 the mutual inductance. 



For potential transformers a high resistance is connected across the 

 primary side and the secondary voltage is applied through the galva- 

 nometer potentiometer fashion to a portion of this resistance. The phase 

 relations are taken care of by inserting a large fixed self inductance in 

 the low side of the resistance and then shunting a fixed condenser around 

 a variable portion of the latter. This has the effect of neutralizing a„ 

 portion of the inductance. 



The vibration galvanometer used was of the Campbell type with a 

 moving coil specially constructed to give high voltage sensitivity. The 

 instrument could detect 0.5 microvolt at 25 cycles. 



The advantages of this method are that only a single instrument is 

 required for all ranges of transformers, but one observer is required, and 

 neither a polyphase source, a phase shifting device nor a rotating com- 

 mutator is required. P. G. A. 



GEOLOGY.— Coal near the Black Hills, Wyoming-South Dakota. R. W. 

 Stone. Bulletin U. S. Geological Survey No. 499, pp. 66, with 

 maps, sections, and illustrations. 1912. 

 The salient features of the Black Hills uplift are: (1) a central area of 

 crystalline Archean and Algonkian rocks; (2) a limestone plateau with 

 in-facing escarpment; (3) a continuous trough, the Red Valley, com. 

 pletely encircling the plateau; and (4) an outer rim of flat-topped ridges 

 sloping away from the central area. The formation^ of which it is 

 necessary to take cognizance in connection with the occurrence of coal 

 are the Spearfish formation (Triassic?), locally known as the "red beds;" 

 the Sundance formation and Morrison shale (Jurassic?) ; and the Lakota 

 sandstone, Fuson shale, Dakota sandstone, and Graneros shale (Cre- 

 taceous). 



