( 31B ) 



sponding position of eqnilibriimi. If on tlie ofher baud there is a 

 certain capacity, tiic detleclion will ie(|iiire some time. 



Tiie wav in which llic inia,i>e of the mirror or in tlie string- 

 galvanometer the qiiai'l/. Ihread Ihen moves, is entirely determined by 

 the wav in wliich a con<lenser is charged or discharged, ('ailing <i 

 the deflection of Ihe galvanometer at the time t aftei- the potential 

 dilference is eslaltlished and .1 the permanent detlection, we have 



( -' 



a = .lVl — '' 



wdiere e is the base of natnral logarithms, c the capacity of the 

 condenser and //•' a resistance of wliich it is easy to give a nearer 

 definition. 



In the closed circuit containing the sonrce and the galvanometer 

 the external resistance be 11',,, the resistance of the galvanometer 

 be 11"/, then, if we neglect the resistance of the \\ ii-es joining the 

 condenser and the galvanometer, we ha\e 



h' = i_^- (1) 



The value ir'c is the time constant of the deflection 



>rr = T. 



Expressing ir' in Ohms and c in Fai-ads, 7' is given in seconds. 



When Ihe deflection of the galvanometer is recorded on a nni- 

 forndy moving plane, a curve will be obtained which is the ex- 

 pression of an exponential function and which agrees entirely with 

 the wellknown normal or standardisijig curves of the ca[)illary 

 electrometer^). 



The constants of the cnrve, besides being determined by the rate 

 of motion of the recording plane and the amplitude of the deflection, 

 will depend only on the value of 7\ By changing fc' and r we 

 can regulate the valne of 7' at will. This meaiis that we are able 

 to i-etard or damp the deflection of the galvanometer to any extent. 



The reasoning given is confirmed by the observations. As an 

 example we reprodnce three cnr\es, figs. 1 — 3 of the plate, recorded 

 by the string-gahanometer ■'). The connections are schematically 



1) See e. g. W. Elnthovex, Pflüger's Arch. i'. d. gesammle Physiol. Btl. ."iG, 

 p. ü28. 1894. And „Onderzoekingen" Physiol. Jaboiat. Leyden, 2nd series I. 



~) See W. Elnthovex, Ann. der Phys. 12. p. 1051). 1903 and 14. p. 182. 1904. 

 Also in Kon. Akad. v. Welenscli. te Amsterdam, Piepoil of the meeting of June 27, 

 1903 and March 3Ü, 1904. 



