On the Measurement of Magnetic Forces. 447 



determined. The observed numbers are all nearer the Green- 

 wich values than those deduced as above. 



Postscript. — To obtain satisfactory accordance between 

 observations of deflection at short distances, it is desirable to 

 take count of additional terms in the series proceeding by 

 pow r ers of r~ 2 . The complete formula then stands, 



2M r 3 tan 6 



where 



A 2 = 2L 2 , A 4 = 3L 4 , A 6 =4L 6 . 



The agreement thus obtained between long and short distances 

 is quite satisfactory. 



L. On the Measurement of Magnetic Forces by means of 

 Hydrostatic Pressure. By G. Quincke *. 



I. 



I COMMUNICATED to the Berlin Royal Academy of Sci- 

 ences last April f the results of an investigation of the 

 pressures exhibited by insulating liquids in an electric field, 

 when they are electrified like the glass of a Ley den jar. 



The general result obtained was the production of a tension 

 parallel to the lines of electric force, and of a nearly equal 

 pressure at right angles to the lines of electric force, which 

 were proportional to the square of the electric force at the 

 point of the electric field in question, and proportional to the 

 dielectric constant of the fluid experimented upon. 



I have now completed a similar investigation for magnetic 

 and diamagnetic fluids, employing, to some extent, similar 

 methods. If dielectric and magnetically polarized substances 

 behave similarly, as is required by the theoretical views of 

 Faraday %, Maxwell §, and Helmholtz ||, we must have with 

 magnetic fluids under the influence of magnetic forces, just 

 as with insulating fluids under the influence of electric forces, 

 a pressure produced at right angles to the lines of magnetic 

 force of the magnitude 



where Hi is the magnetic force at the point of the magnetic 



* 



J Translated from the Berliner Sitzungsberichte of January 17, 1884. 

 t Berl Sitzungsber. 5 April, 1883, pp. 413-420 ; Phil. Mag. xvi. p. 1. 

 % Faraday, Exp. Kesearches, §§ 1224, 1297, 1731-36, 2846, 3256, 

 3266-68. 



§ Maxwell, " Electricity and Magnetism,' 2nd ed. ii. p. 257, § 642. 

 || Yon Helmholtz, Wissensch. Abh. i. pp. 800 & 813. 



2H2 



