652 report — 1884. 



mercury of the Clark cell. No mercurous sulphate is employed, the liquid being 

 simply a saturated solution of zinc sulphate. 



if the same kind of amalgam he used for both poles, the symmetry is complete, 

 and there should be no E. M. F. But if we take for one pole a strong, but fluid, 

 amalgam", and for the other the same amalgam diluted with an equal volume of 

 pure mercury, we find a very sensible E. M. FT, the strong amalgam correspottding 

 to the zinc of the ordinary Clark. In my experiment the E. M. F. was -004 Clark, 

 and remained pretty constant from day to day. In another cell the same strong 

 amalgam was used for one pole, and for the other pole was diluted with three times 

 its volume of pure mercury. In this case the E. M. F. was "009 Clark. 



If we replace the diluted amalgam with pure mercury, we obtain (without 

 mercurous sulphate) nearly the full E. M. F. of the Clark cell, but, as might be 

 expected, the lorce is very unsteady. From this it would seem that the function of 

 the mercurous sulphate in the usual form of cell is to retain the purity of the 

 mercury, and that the E. M. F. is largely due to the affinity of mercury for 

 zinc. 



4.- On an Analogy between Heat and Electricity. 

 By Professor G. F. Fitzgerald, F.B.S. 



The object of this communication was to point out the analogy that may be 

 drawn between quantity of electricity and quantity of entropy when electric 

 potential is considered as analogous to temperature. A non-conductor of electricity 

 would be a non-conductor of entropy, which is the same as a non-conductor of 

 heat. A conductor would be a heat engine in which the fall of temperature of the 

 entropy was completely utilised. 



It was pointed out that a molecular structure of the ether could be assumed 

 which would not conduct heat as material gases do, but which might be thrown by 

 differences of temperature into the State of stress that explains electrostatic pheno- 

 mena. It was explained that this was a step beyond that made by Maxwell in his 

 Electricity and Magnetism, where he avoids any hypothesis as to how electric 

 displacement produces mechanical stress. It was, on the other hand, explained 

 that the principal object of the paper was not to bring forward this very doubtful 

 hypothesis, but to point out that the analogy of electric currents and displacements 

 to the motion of an incompressible fluid was by no merais the only one that could 

 be drawn, and by pointing this out, to obviate the danger which is at present 

 imminent of this mere analogs - being considered as a likeness. 



5. The Telemeter System. By J. Urquhart Mackenzie. 



0. The Influence of an Electric Current on the Thinning of a Liquid Film. 

 By Professors A. W. Reinold and A. W. Rucker. 



The authors described the effect of passing a current of from 0-5 to 1 5 micro- 

 amperes through a cylindrical liquid film. The films were about 40 mm. long and 

 33 mm. in diameter, and were formed of a solution either of common potash soap, 

 or of Plateau's ' liquide glycerique,' with a small quantity of nitrate of potash added 

 to improve the conductivity. A number of films were formed, and allowed to thin 

 under the action of gravity alone, when no current flowed. They all behaved 

 substantially in the same way. After a few minutes signs of colour were seen at 

 the top, and in from 9 to 15 minutes a complete ring of black appeared. Three 

 quarters of the film were colourless. When a downward current was passed 

 through a film from the moment of its formation, rings of colour appeared with 

 great rapidity, but much broader and more diffuse than before, and occupying a 

 larger area of the liquid. If the film had already a ring of black at the top, the 

 effect of the downward current was to augment this, and rapidly to thin the 

 portion immediately below it. In all cases, provided the current was not too 



