46 Prof. J. Burdon-Sanderson. Relation of Motion in Animals 



curve, and an electrical change, which we record photographically. 

 Diagram 4 will serve to explain what (as will be immediately seen) 



Diagram 4. 



Explanation of Diagram 4. — The horizontal line 

 is that of equipotentiality of the two surfaces of 

 contact p and d. The curve P' expresses the rela- 

 tive negativity (negative difference of potential) of 

 the surface p ; the curve D' the corresponding rela- 

 tive negativity of the surface d. S is a curve of 

 which the ordinates are the algebraic sums of the 

 corresponding ordinates of P' and J)'. 8 is the 

 photographic curve which expresses S' ; P' is the 

 photographic curve which expresses P. The num- 

 bers under the horizontal line indicate hundredths 

 of a second. The distance 1 1' expresses the time 

 taken by the wave in its progress from p to d. 



actually happens at the moment the wave passes under p. It means 

 that a current suddenly appears there, of which the direction is from 

 p to d. When the wave reaches d, a second effect of the same kind (D') 

 occurs, of which the direction is opposed to the first. What the gal- 

 vanoscopic effect of this must be is easily understood from Diagram 4, 

 in which the two curves P' and H are placed in a relative position to 

 each other which expresses their time-relation. The two effects sum 

 together. In the diagram the curve S' expresses the result of that sum- 

 mation, i.e., the actual variations of difference of potential between the 

 contacts which occurred while the wave was passing from p to d. It 

 will be seen at once why we call this effect the diphasic variation. 



I explained before, that in accordance with the fundamental pro- 

 perties of our instrument the curve P would have as its photographic 

 expression the curve P. Similarly the combination-curve S', would 



