538 Royal Society. 



to the entire distance between two contiguous stria?, when it will 

 apparently be reduced to zero ; the striae will then again appear 

 stationary. Experiments appear to confirm this view of the case. 



Experiments were next instituted with a view of ascertaining the 

 connexion between the flow and resistance. Starting from a con- 

 dition of current and break for which the striae were stationary, it 

 was found that an increase of resistance, introduced generally in 

 the primary circuit, produced a forward flow, i. e. from the posi- 

 tive towards the negative terminal, while under similar circum- 

 stances a decrease of resistance produced a backward flow. Fur- 

 thermore, if after producing a forward flow the resistance be 

 continually increased, the flow after increasing in rapidity so as 

 to become indistinguishable by the unassisted eye, gradually appears 

 to become slower, and ultimately to reverse itself, in accordance with 

 the law suggested above. 



Another form of contact-breaker was also occasionally used. 

 The principle upon which it was based was the sudden disruption 

 of a thin film of conducting liquid by a discharge between the 

 electrodes of a circuit. The mode of effecting this was to make 

 one electrode terminate in a platinum plate fixed in a horizontal 

 position, and supplied with a uniform film of dilute sulphuric acid ; 

 the other in a platinum point, the distance of which from the plate 

 is capable of delicate adjustment by means of a screw. Electro- 

 motive force required for this break is not less than that of 5 cells 

 of Grove. 



As soon as the current passes, the fluid between the plate and 

 point will be decomposed and electrical continuity broken. This 

 done, the fluid flows back again, and continuity is restored. By 

 a proper adjustment of the supply of fluid and of the distance of 

 the electrodes (the latter varying from -05 inch to *001 inch), the 

 number of disruptions may be made to attain 1000 per second. 



The currents delivered by this form of break are exceedingly uni- 

 form, and the effects produced are quite equal in delicacy to those 

 produced by the electromagnetic or by the wheel break. 



The elements used in the battery to which aUusion was made in 

 the early part of this paper are zinc and carbon. The zinc is 

 immersed in dilute sulphuric acid in the proportions of 1 volume 

 of acid to 7 of water ; and the carbon in a saturated solution of 

 bichromate of potash with 1 volume of sulphuric acid to 7 of the 

 solution. The carbon and bichromate solution are held in a 

 porous cell. 



The absence of nitric acid permits this battery to be used in a 

 room ; while the fact that the zinc is attacked only when the circuit 

 is complete, renders it unnecessary to lift the plates out of the fluid 

 when not in use, as in the bichromate battery. The only limit to 

 the time during which this battery may be left untouched, appears 

 to be the period when the bichromate salt finds its way into the 

 outer cell, so as to attack the zinc independently of electrical action. 

 But this does not take place to an extent materially to affect the 

 action for some months. 



