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Mr. G. J. Burch. On the Interpretation of [Feb. 11, 



I. Variations of Potential Difference bekveen Two Points of a Linear 

 Conductor traversed by a Source of E3LF. 



In the accompanying diagram (fig. 1) the successive stages of the 

 electrical condition are represented graphically, and arranged in order 

 of time. An electromotive force is supposed to originate at the 

 point P, from which it spreads in both directions, the shaded portions 

 indicating the parts in which it exists, and those not shaded the parts 

 not yet reached by it, or no longer affected. The shaded parts may 

 therefore be considered as positive to the unshaded. After a certain 

 interval the effect subsides. This is represented as occurring first at 

 the point from which it originated. Obviously, if the duration of the 

 active period is the same for each point of the linear conductor, the 

 time curve of the subsidence of the wave of E.M.F. will be parallel to 

 its development. It does not, however, necessarily follow that it must 

 be so, and hence the cessation of electrical activity may be more con- 

 veniently represented as a separate function of the time. 



p 



Fig. 1. — Diagram, showing the successive positions of a wave of electromotive 

 activity originating at the point P of a nerve-fibre, and travelling outwards in 

 both directions. The shaded portions are positive to the unshaded. 



The general effect of varying the rate at which the electrical change 

 is propagated, and its duration in various parts of the linear con- 

 ductor, is shown in figs. 2 to 7. They are drawn on the same plan as 

 fig. 1, that is to say, time is reckoned from above downwards, and 

 position on the linear conductor horizontally. The excitation is 

 supposed to take effect at the centre of the conductor, and to spread 

 symmetrically to the right and to the left. But in order to show more 

 forcibly the relation between the above-mentioned two modes, of 

 expressing the problem, the right-hand half of each figure represents 

 the electrical change as a wave passing along the conductor, while the 

 left-hand half gives the commencement, duration, and end of the 

 electrical activity at a series of points on the conductor. 



The relation of the electrical changes to variations of potential 

 difference between any given pair of leads may be studied by drawing 

 a pair of vertical lines the required distance apart on tracing cloth, 



