300 £. L\ Williams — Kh'ctroiiuxpn'tic Effect. 



the poles as shown in fig. 3, there is a rise of the mercury in 

 the vertical tube no matter what the direction of the current 

 and the magnetic field may be. Here the force acting upon 

 the current in the mercury is normal to both the vertical and 

 horizontal columns no matter what the direction of the current 

 and the magnetic field. This lateral pressure on the sides of 

 the horizonal tube acts hydrostatically and forces the mercury 

 up in the vertical tube, as that is the only place that the pres- 

 sure may manifest itself in a movement of the mercury. 



In another form of tube he had four lateral tubes attached 

 to the horizontal one. Fig. 4 shows the arrangement with 

 horizontal tube end on. When the current flowed toward the 

 reader and the field was in the direction indicated, the mercury 

 rose in B, fell in C and momentarily rose in A and D. This 

 momentary change in A and D was simply an inertia effect 

 due to the changes in height of mercury in B and C. 



In connection with this behavior of a mercury or liquid con- 

 ductor carrying a current in a magnetic field, it is well to keep 

 in mind the distribution of the lines of flow through the hori- 

 zontal tube past the openings in the lateral tubes. This point 

 was investigated in the following way : A conducting sheet of 

 an electrolyte (acidified water) was arranged in the form which 

 w r as the cross-section of the tube used by Bowden and shown 

 in fig. 5. This cell was formed by sticking strips of hard rubber 

 to a plate of glass. The lines of flow were obtained by the 

 usual method employed in the laboratory, viz., using the sec- 

 ondary of an induction coil for the source of E. M. F. and a 

 telephone receiver to locate the equipotential points. The lines 

 of flow curve out into the opening of the lateral tubes as shown 

 in fig. 5. After trying out the apparatus, similar in form to 

 that used by Bowden, my attention was called to Lippmann's 

 galvanometer* and its application by Leducf and DuBois:}: in 

 measuring magnetic fields. In principle their apparatus aud 

 Bowden's are one and the same. Fig. 6 is a schematic view of 

 Leduc's apparatus. It differs from Bowden's in this respect, 

 that the vertical central tube, C, extends below the horizontal 

 tube, and the current is sent through the vertical column 

 instead of the horizontal one. In Leduc's apparatus the col- 

 umn of mercury carrying the current was inclosed by two par- 

 allel plates, placed very close together with lateral openings for 

 the tubes A and B, fig. 6. Bowden made his apparatus from 

 glass tubing, and as a cross of the form in fig. 6 is easily made 

 by sealing glass tubing together, it seemed worth while to see 

 how satisfactorily a tube might be made for measuring mag- 

 netic held strengths instead of the flat cell used by Leduc and 



* Lippmarm, Jour. d. Phys. (2), vol. iii. p. 384, 1884. 

 + Leduc, Jour. d. Phys. (2), vol. vi, p. 184, 1887. 

 % DuBois, Wied. Annal., vol. xxv, p. 142, 1888. 



