>52 Prof. (J. Quincke on I he Measurement of Magnetic 



in the electric Held become doubly refractive, whereas no 

 double refraction could be detected m magnetic fluids in tlio 

 magnetic Held, is in harmony \\\i\\ the difference already 

 mentioned between electric and magnetic forces. 



II. 



If follows from those experiments that, underthe influence 

 of magnetic forces, the hydrostatic pressure at the bounding- 

 line of air jiikI magnetic or diamagnetic fluids, parallel and at 

 rio ht, angles to the linos of magnetic force, suffers the same 

 increase or decrease ; that the pressure resulting from the 

 magnetic forces is of equal magnitude parallel and at right 

 angles to the lines of magnetic Force. 



In a homogeneous !luid in a magnetio field of constant 

 magnetic force the magnetic pressures must be in equilibrium. 

 There can only be a difference of pressures at the boundary 

 of two heterogeneous fluids. 



I have measured this difference of pressure for various 

 magnetic and diamagnetic fluids at the bounding-surface 

 with atmospheric air in [J-shaped glass tubes, when the fluid 

 in the vertical narrow limb of the U-shaped tube was plaoed 

 between the vertical pole-surfaces of the Berlin electro- 

 magnet in a magnetic Held of the constant magnetic force Hi, 

 the other wide limb being outside of the magnetic field, or in 

 u magnetic Held of magnetic force 0. 



The D-shaped tube was adjusted until the fluid meniscus 

 was in the middle of the magnetic field* Upon interrupting 

 the exciting current, the level of a magnetic fluid sank, and 

 the level of a diamagnetic fluid rose, by an amount A, and 

 the pressure decreased or increased by an amount 



//<x=MIf (8) 



ha expresses the pressure in grammes on a square centimetre; 

 if A is expressed m centimetres, \\ x is also expressed in the 



O.GkS. system ; r corresponds to the quantity ■ ' - of equa- 

 tion (2). * (S7r 



The magnetio increase in heights in my measurements 

 attained tne magnitude 32 millim. and more with magnetic 

 fluids; — 0*7 milhm. with diamagnetic fluids. In thecaseofthe 

 smaller heights, the measurements were made with a catheto- 



mefor-microseopo; for the greater heights, an ordinary eathoio- 



meter wad employed. 



With an electromagnet belonging to the Carlsruhe Poly- 

 technic, excited by an electro-dynamic machine and manga- 

 nese-sulphate solution of spec.gr. 111()5 ? between square 



