iv ELECTROMOTIVE ACTION IN MUSCLE 409 



electrometer by a total shifting only, without oscillations, although 

 unequal variations of current are present which fail to appear 

 in the meniscus, because the oscillation frequency is either too 

 high for the existing E.M.F., or too low in proportion with the 

 electromotive frequency. There are two ways of recording the 

 rapid oscillations of the meniscus ; the beats may be photographed 

 on a rapidly -moving sensitive plate, which is not difficult with 

 the present development of instantaneous photography (unfor- 

 tunately no methodical investigation of the action currents in 

 skeletal muscle has yet been undertaken in this manner) : or 

 the form and time-relations of the movements of the meniscus 

 may be read off directly by the stroboscopic method. 

 Martins (I.e. p. 590 ff.) attached a paper flag, 1 cm. square, 

 instead of a writing -point, to the lever end of a very 

 sensitive electro -magnetic Pfeil's chronograph. If this instru- 

 ment is introduced into the circuit of the interrupter, the lever 

 will swing in the period of the interrupting spring. The paper 

 flag, at a sufficient frequency, exhibits a broad, gray margin at its 

 upper and lower edges, while the flag itself appears quiescent. 

 If the oscillating meniscus of the capillary electrometer is 

 observed through the lower or upper margin, its oscillations 

 vanish altogether, and it appears sharp and fixed if it and the 

 flay are vibrating at the same period. !NY>w since both oscillations 

 are produced by the same interrupter, it is obvious that the 

 mercury has no intrinsic vibration period, but exactly repeats 

 the oscillations of the interrupter ; seeing that every frequency 

 of the latter (up to 100 per sec.) obliterates the vibrations, i.e. 

 gray film, of the meniscus, as previously visible in the 

 stroboscope. It is clearly easy with this method to determine 

 objectively the unknown frequency of periodic variations of 

 current, read off in the oscillations of the meniscus, if two inter- 

 rupters are used, one of which is connected with the capillary 

 electrometer, the other with the stroboscope in a separate 

 circuit. If the vibration period coincides in the two interrupters, 

 the oscillations of the meniscus are neutralised. If they differ, 

 interferences arise, from which it is easy to calculate the am- 

 plitude of difference in vibration in the two springs (Martius, I.e. 

 p. 591). Let the rate of vibration in the stroboscope be 18 per 

 sec. If, instead of frequent oscillations of the meniscus (which 

 can only be counted artificially), two regular beats are observed 



