THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



NO V EMBER 1878. 



XLIV. On the Experimental Determination of Magnetic Mo- 

 ments in Absolute Measure. By Thomas Gray*, B.Sc, 

 Thomson Experimental Scholar in the University of 

 Glasgow f . 



[Plate V.] 



SOME experiments on the intensity of the earth's mag- 

 netism were made by Gauss, and published, under the 

 title "Intensitas Vis Magneticae Terrestris ad Mensuram 

 Absolutam Revocata," in the Comment ationes Societatis Got- 

 tingensis, 1832, and in a paper on the General Theory of 

 Terrestrial Magnetism, an English version of which is given 

 in the second volume of i Taylor's Scientific Memoirs.' 



The results are given (according to the system the impor- 

 tance of which was first seen, and which was first introduced, 

 by Gauss himself) in absolute measure. The units of length, 

 mass, and time employed by him are the millimetre, milli- 

 gramme, and second. His results, when reduced to O.G.S. 

 units, show that a steel magnet with which he experimented 

 had a magnetic moment of 22*2 per gramme mass. 



Gauss also calculated (Taylor's Scientific Memoirs, vol. ii. 

 p. 225) the mass of steel which would have to be placed in 

 each cubic metre of non-magnetic matter in order to make up 



* Now Demonstrator in Physics and Instructor in Telegraphy in the 

 Imperial College of Engineering, Tokei, Japan. 



t Being the Essay to which the Cleland Gold Medal was awarded 

 by the University of Glasgow in the Session 1877-78. Communicated 

 by Sir W. Thomson to the Philosophical Magazine by permission of the 

 Senate. 



Phil Mag. S. 5. Vol. 6. No. 38. Nov. 1878, Y 



