252 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



is produced, by the pitch of which the current strength may- 

 be determined. To obtain accurate results with the appa- 

 ratus, corrections for temperature and pressure must be ap- 

 plied. 



Hasra at Strasburg and Clark at Heidelberg have investi- 

 gated the electromotive force produced by the flow of water 

 through capillary tubes, using a quadrant electrometer to 

 measure the difference of potential. Clark finds that the 

 electromotive force is greater the narrower the tube ; that in 

 very narrow tubes it is independent of the length; that dif- 

 ferent electromotive forces appear if the interior of the tube 

 be coated with different substances ; that the electromotive 

 force decreases with the time ; and that the seat of the elec- 

 tromotive force is the limiting surface of the liquid and the 

 solid tube wall. Hajya finds that the electromotive force is 

 proportional to the pressure, independent of the length of 

 the tubes, dependent on the nature of the inner surface of 

 the tube, increases with the resistance of the water, and 

 probably also with the temperature. The two results agree 

 closely. 



Lippmann has contrived an ingenious method of detecting 

 minute quantities of a metal in solution, founded on the 

 principle that when an electrode made of a given .metal is 

 placed in a solution, it will be depolarized only if a salt of 

 that metal exists in the solution. Hence, for example, if a 

 copper wire conveying a weak current be made the nega- 

 tive electrode in any solution, it will be polarized if there is 

 no copper dissolved in this solution, but it will not be polar- 

 ized if the liquid contain one five-thousandth of copper sul- 

 phate. The polarization is easily detected by closing the 

 circuit through a galvanometer, the battery being left out. 

 A contrary deflection indicates polarization. For silver, the 

 sensibility seems somewhat greater. 



Bornstein has experimented to determine the influence of 

 light upon the electric resistance of metals, and gives the 

 following as his conclusions : 1st, the property of having the 

 resistance to an electric current diminished by the action of 

 light is not limited to the metalloids selenium and tellurium, 

 but occurs also in platinum, gold, and silver, and hence most 

 probably in all the metals; 2d, an electric current lessens 

 the conducting power of a conductor as well as its sensibili- 



