Experimental investigations 42 1 



of this instrument was sufficiently prompt to register the number of the separate 

 currents of which the "continued discharge" of the Torpedo consists. It was 

 not, however, sufficiently sensitive to trace the curve of the intensity of the 

 current when the strength of the current was less than that required to work 

 the tracing point, and the trace therefore represents only the phases of greatest 

 strength of current in each separate discharge. 



M. Marey calls each separate discharge of the Torpedo an electric flux. 



The whole discharge consists of a rapid succession of these fluxes, at the 

 rate of from 60 to 140 per second, gradually decreasing in intensity, but re- 

 maining sensible sometimes for a second or a second and a half. In one of the 

 tracings 120 fluxes may be counted quite distinctly, with a somewhat irregular 

 continuation of feebler fluxes. 



The electromagnetic signal, however, depending on the attraction of a soft 

 iron armature, is acted on by a force varying nearly as the square of the strength 

 of the current. It is therefore unable to respond to feeble currents, and it does 

 not indicate the direction of the currents, even when improved in certain par- 

 ticulars by M. Marey. 



The third indicator used by M. Marey was the capillary electrometer of 

 M. Lippmann. In this instrument a capillary glass tube is filled in one part with 

 mercury and in the other with dilute sulphuric acid. The pressure of the mercury 

 is so adjusted that the division between the two liquids appears in the middle 

 of the field of a microscope. The electrodes of the instrument are connected 

 with the two liquids respectively, and when a small electromotive force acts 

 from one electrode to the other, the surface of separation of the two liquids 

 is seen to move in the same direction as the electromotive force, that is to say, 

 the mercury advances if the electromotive force is from the mercury to the acid, 

 and retreats if it is in the opposite direction. 



This instrument, therefore, is admirably suited for the investigation of small 

 electromotive forces, and the mass of the moving parts is so small that it responds 

 most promptly to every variation of the electromotive force. Its only defect 

 is that its range is limited to the electromotive force required to decompose 

 the acid, and the electromotive force of the Torpedo, as we know, is of far 

 greater intensity than this. M. Marey therefore used a shunt, so as to diminish 

 the force acting on the electrometer to such a degree as to be within the working 

 limits of the instrument. 



He thus ascertained that the back of the fish is positive with respect to the 

 belly, not only on the whole, but during every phase of each flux, and that it 

 does not sink to zero between the fluxes. 



The modern researches on the electric fishes would seem to point to the 

 conclusion that the electric organ is not like a battery of Leyden jars in which 

 electricity is stored up ready to be discharged at the will of the animal, but 

 rather like a Voltaic battery, the metals of which are lifted out of the cells 

 containing the electrolyte, but are ready to be dipped into them. 



