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Physics. — “On the Theory of LiPPMANN’s Capillary Electrometer”’. 
By Prof. W. EINTHOVEN (Communicated by Prof. T. ZA AER.) 
In a paper on the capillary electrometer and on the action currents 
of the muscle HERMANN!) has put forward the statement, that the 
results obtained by Burcu*) and myself*) in the investigation of 
the motion of the mercury in the capillary electrometer are imme- 
diate consequences of his theory, and that since Burcu and I should 
have obtained empirically our results, they ought to be regarded as 
a „schöne Bestätigung”’ of his theory. An answer of Burcu“) here- 
upon has already appeared. 
In answering HERMANN I will try by means of some new expe- 
riments to advance somewhat our knowledge of the laws governing 
the motion of the mercury in the capillary electrometer. 
On a former occasion I have given the equation: 
be = C (y*— 1 
gr he ea 
where C is a constant, y the distance the meniscus has moved from 
its zero position at the time 7 and 4* the distance the meniscus 
would have moved if the P.D, of the poles of the capillary electro- 
meter at the time Z had been constantly applied. 
In order to obtain for all capillary electrometers comparable values 
of the constant, we shall in this paper always measure the time 7 
in seconds ®), whereas y and y* will be given in arbitrary but equal 
units. The value of C is apparently unaffected by a change of the 
unit in which y and y* are measured. The constant C is, as I re- 
marked on a former occasion, determined by the properties of the 
instrument, especially by the mechanical friction in the capillary 
and the ohmic resistance w in the circuit; the precise relation 
between C and w 1 did not mention till now, but it will be given 
in. the following. 
HERMANN ate that the mentioned relation is very simple, and 
assumes that C varies as the inverse of w. The equation his theory 
1) Prrücer's Arch. f, d. ges. Physiol. 1896, Bd. 63, S. 440. 
2) Philosoph. Transact. of the Royal Soc. London, 1892, Vol. 183, p. 81. 
3) PrrüGer's Arch, f. d. ges. Physiol. 1894, Bd. 56, S. 528 und 1895, Bd. 60, S. 91. 
4) Proceedings of the Royal Soc. London, 1896, Vol. 60, p. 329. 
5) In formerly given calculations of the constant, the time was given in twentieth 
to fiftieth parts of a second dependent on the velocity of the photographic plate, on 
which the normal curves were recorded, being 20 to 50 mm. per second. 
