THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



JANUARY 1899. 



I. The Magnetic Fluxes in Meters and other Electrical 

 Instruments, By Albert Campbell, B.A* 



IN all electrical measuring instruments in which the de- 

 flecting or controlling forces are electromagnetic, the 

 magnetic fluxes and fields are of great importance, and yet 

 there seem to be no tables published which give even rough 

 measurements of these, the result being that many people 

 who are thoroughly expert in the use of instruments have 

 no idea whatever of the order of magnitude of the magnetic 

 fluxes occurring in the very commonest instruments. In 

 order, therefore, to fill this gap to some extent, I have 

 recently carried out a series of experiments on the subject, 

 and although the list of instruments thus tested is not very 

 extensive or complete, I have been able to include in it a 

 good many of the more familiar types. As individual instru- 

 ments of the same type vary somewhat amongst themselves, 

 it would have been waste of time to have aimed at great 

 accuracy in these measurements. Accordingly, whilst guard- 

 ing against large errors in general, I have been content in 

 one or two cases with results which only indicate the order 

 of magnitude of the quantity measured. 



In most cases the quantity determined has been B, the 

 magnetic flux density or number of induction-tubes per square 

 centimetre sometimes through iron, sometimes through air. 



* Communicated by the Physical Society : read Oct. 28, 1898. 

 Phil. Mag. S. 5. Vol. 47. No. 284. Jan. 1899. B 



