392 Einthoven and Jolly 



The absolute amounts are — 



For summit A .... —15 microvolts. 

 B . . . .150 



„ C . . . . 230 



In proportion to B, both A and C are greater than in fig. 3. 



If the illumination is weaker and continued for some time, then one 

 observes at the moment when darkening begins after a latent period, a new 

 elevation of the curve, an off-effect A^. 



In fig. 5 there is given an example. In photographing the movements 

 of the string, the sensitive plate is here moving more quickly, so tjiat in the 

 system of co-ordinates 1 mm. abscissa is now equal to 0-2 sec. The sen- 

 sitiveness of the galvanometer is regulated in such a way that 1 mm. 

 ordinate amounts to 20 microvolts. This is visible in the control curve, 

 which is obtained at the end of the curve by suddenly introducing into 

 the circuit a potential difference of 200 microvolts. The intensity of the 

 illumination is 10~* Ig, while the duration of illumination as indicated 

 by the signal amounts to 4*58 sec. 



The latent period of the preliminary deflection A is 01 sec, that of the 

 off-effect Aj is 1*8 sec. 



The absolute amounts of the potential differences are — 



For A . . . . - 20 microvolts. 

 „ B 384 „ 



„ C 670 „ 



The potential difference of A^ cannot easily be given. It may be 

 estimated at 60 microvolts, and is measured after connecting the beginning 

 and end of the curve A^ by a line running in the course of the main curve. 

 We may remark here that the off-effect Aj is in general higher the longer 

 the illumination has been continued. 



Further, we draw attention to the fact that the curves in figs. 3, 4, and 

 5, although they may differ in details, are yet formed essentially in pre- 

 cisely the same way» It may also be remarked that fig. 15, which we shall 

 discuss later, shows no essential difference from figs. 3, 4, and 5. 



2. The Three Substances. 



The oomplicated structure of the curves above described and the striking 

 fact that a deflection in the same direction takes place both on illumination 

 and on darkening, suggest that there are in the eye two or more different 

 processes occurring partly simultaneously, partly successively, whose fusion 

 determines the form of the electrical reaction. 



Further investigation confirms this suggestion, and if recourse is had to 

 very weak or very strong light, it seems even to be possible to bring about 

 a separation of the supposed processes. The phenomena are explained in 



