(317 ) 



Fia-. 2. 



ropreson<(Ml in (!<>•. •}. Here E 

 is ;i hullerv, N ;i key, ^/ llie 

 striiijLi-fiiihaiioineler and r' llie 

 eoiideiiser, .4, B aiid Zi repro- 

 sentiii,!»' resislaiK-es. Tli<> sejisi- 

 liveiioss of llie uahniioineler lias 

 heen l<e])l ahoiil (Mpial iii llie 

 lliree cases so llial a defleolion 

 of' J niiii. corresixiiids lo a 



(Mirreiit of 2y<lH)-' Anip., llie eleciroinotive foree /J of llie l»atl('r>- 

 and Ihe resistances A, B and R being so chosen I hat when I he 

 cm-rent is jiassed a permanent deflection of 20 mm. is obtained. The 

 rate of motion of the recording plane is 500 mm. per second. Hence 

 in the net of s(piare millimetres on the plates ^) I mm. of absciss 

 = 0.002 sec. and 1 mm. ordinate = 2 X 1^^~" ^^'i'l>- '^''t' circuit 

 was automatically made and broken at /S' by an arrangement all ached 

 to I he recording ])lane. 



For // a carbon resistance was taken with large resistance and 

 B was small compared with R. W, could be put eipial to /? wilhonl 

 an appreciable error. In tigs. 1 and 2 of the plate \]\ was J. 11 

 megohm, whereas ITg in tig. 3 amounted to 117000 ohms. The 

 resistance of the galvanometer W; was 8600 ohms. 



In tig. 1 of the plate the capacity of the condenser is 0. The 

 string is seen to make oscillatory movements -with a period of about 

 1,3 mm. = 2.6ö •'). 



These movements are damped liy inserting a certain capacity in 

 the condenser. In tig. 2 of the plate that capacity is 0.94 microfarad, 

 in tig. 3 of the plate 0.2 microfarad. 



Calculating the value of //;' from Wi and W^ by formula (1) and 

 then the time constant T-=iöC, the time constant of fig. 2 is found 

 to be 8.0 (J, and that of tig. 3 1.6^7 and it is clear that the amount 

 of retardation or of damping is determined l)y the value of the 

 time constant. 



For clearness' sake we started in the abo\e reasoning from the 

 simplest case and assumed that the mass ni of the string and the 

 forces which independently of Ihe condenser damp its motion and 

 which w^e will collectively indicate by y, may be neglected. Thi.s 

 hypothetical case will the more closely agree with reality, the larger, 

 other condilions being (Mpial, T is taken. Hence in this resjiect lig. 2 



1) On the way of ii-ci)r(ling and IIh.' nel of square inillinietres see Annalen ilcr 

 Phys. 1. c. 



2) 1 (T = Ü.Ü01 sec. 



