1902.] 



A Theory of the Capillary Electrometer. 



221 



unexcited nerve-fibres which surround the active fibres near the proximal end r 

 shunts part of the current. 



This curve should be compared with No. 1535 in fig. 14, in which 

 the wave of electrical response is longer than the distance between^the 

 leads, and consequently the first phase is due entirely to the develop- 

 ment, and the second to the subsidence, of the E.M.E. 



The material discussed in this paper consists mainly of some 1900 

 photographs of the electrical response of nerve, taken in the Physio- 

 logical Laboratory, Oxford, by Professor Gotch and myself. I have 

 made full analyses of more than 150 of the curves, and have measured 

 the principal points of a much larger number. 



Many other examples could be given, but I have in each case 

 selected the one best suited, either from the sharpness of the definition 

 or the completeness of the data, to illustrate the theory. It has' 

 become evident from a comparison of the photographs, that the values 

 of v, 6, 7T, and hr, are greatly affected by temperature and the condi- 

 tion of the preparation ; but as these involve the physiological side of 

 the problem, which will be dealt with by Professor Gotch, I have for 

 the present confined myself to showing the methods by which they 

 may be determined. 



" Contributions to a Theory of the Capillary Electrometer. I. — On 

 the Insulation Eesistance of the Capillary Electrometer, and 

 the Minimum Quantity of Electricity required to produce a 

 Visible Excursion." By George J. Buech, M.A. Oxon. r 

 E.B.S., Lecturer in Physics, Eeacling College, Eeading. 

 Received April 17 —Read May 1, 1902. 



What may be called the Insulation Resistance of the capillary 

 electrometer is important for two reasons — first, as to its bearing on 

 the theory of the instrument, and secondly, as affecting the method of 

 using it in dealing with electrical charges or quantities of limited 

 amount. I propose briefly to record some of my own experiments on 

 this head. 



In many capillary electrometers, if an excursion of the meniscus is 

 produced by touching the terminals with a source of electromotive 

 force and then removing it, leaving the circuit open, the meniscus 

 returns in a comparatively short time to the position it would occupy 

 if the instrument were short circuited. In other words, the charge, 

 which, as Lippmann showed, is contained in the instrument as long as 

 the meniscus is deflected from its zero position, gradually leaks away. 

 The question naturally arises, whether this leakage is accidental like 



