ABSTRACTS 



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

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

 Each of the scientific bureaus in Washington has a representative authorized to 

 forward such material to this journal and abstracts of official publications should 

 be transmitted through the representative of the bureau in which they originate. 

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

 this issue. 



PHYSICS. — A study of electromagnet moving coil galvanometers for 

 use in alternating current measurements. Ernest Weibel. Bureau 

 of Standards Scientific Paper No. 297 (Bull. Bur. Stds., 14: 23-58). 

 1917. 

 This paper gives the results of a study of the electromagnet moving 

 coil galvanometer that has led to the construction, of instruments 

 with sensitivities much greater than those previously obtained and 

 equal to those of the best direct current moving coil galvanometers. 

 The theory of the instrument is developed. The equation of motion 

 is first expressed in terms of the intrinsic constants (the moment of 

 inertia, the moment of damping, the moment of restoration, and the 

 moment of displacement) and the deflection, velocity, acceleration, and 

 current in the moving coil. The current is then known from the 

 resultant electromotive force in the moving coil circuit and the latter's 

 constants. It is necessary in computing the resultant electromotive 

 force to consider not only the impressed but also the induced electro- 

 motive force. The latter is in part due to the motion of the coil in 

 the magnetic field, causing electromagnetic damping, and in part due 

 to the alternation of the flux linking with the coil, causing a current 

 which results in a control torque in addition to that of the suspensions. 

 The paper also contains descriptions and gives the performances of 

 four instruments. The results indicate that the theory as given is 

 fundamentally correct and therefore serves as a good basis for the 

 design and use of instruments of this kind. E. W. 



GEOLOGY. — The lignite field of northwestern South Dakota. Dean E. 



Winchester, C. J. Hares, E. Russell Lloyd, and E. M. Parks. 



U. S. Geological Survey Bulletin 627. Pp. 165, with 11 plates. 1916. 



The report describes the geology and fuel resources of parts of 



Perkins and Harding counties in northwestern South Dakota. The 



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