( 320 ) 



preceding, Iml the slriufi- is lii>lijcr lierc, lias a üi-oaler coiKliicliNO 

 resistance and is sliuhlly more stretclied. 



1 mm. al)sciss = (),()()2 sec, 1 mm. ordijiate = 3 X i**""' Amp. 

 )r,n= 17800, ir, = 20000, hence /r' =: 9420 Ohms. 



In lig. 7 liie capacity is ; in lig. 8 it is 0,05 ji/", hence 7'= 0,47 ö. 

 Ill this hitler ]»h(>logram the string shows a turning-point after ahont 

 1,1a exactly on the new position of eqnilil)rinm. It moves hack 

 through 0.9 mm. and then reaches its erpiilibiiiim again and linally. 



If in the measurement of a cui-i-ent one is contented with an 

 accuracy of 3"'„, the result is obtained in 0.8 tj. If an accuracy of 

 0.37,, i>^ wanted, the result is only ohiaiiicd in 2.2 o. 



These examples may ^iirticc to >e(> what can he expected of ilic 

 method. It is ohxious llmt when seeking the exact value of 7' for 

 reaching tlie limit, we were led by theoretical considerations although 

 we could not use a i-igorons formula. One of these considerations 

 was that for a given string and constant resistances, the capacity 

 required for the limit must he the smaller the more strongly the 

 string is stretche<l. For with greater tension of the string the period 

 f of its oscillations becomes smaller and we may expect the wajited 

 value of the time constant T to change iji the same sense as the 

 period t. 



This consideration leads to some paradoxically sounding predictions. 

 So, for example, it is to be expected that the motion of a strongly 

 stretched string that has been made dead-beat by applying the con- 

 denser nieUiod, will become oscillatoi-y again as soon as the tension 

 is diminished and thereby ihe motion is retarded. Such an expectation 

 seems at variance with the expei-ience gained with other galvano- 

 meters, we might say, gained without excei^ion with all instruments 

 in which vibratory motions are observed. 



The result, which was expected with some anxiety, completely 

 confirmed the prediction. A ipiartz-thread of such a tension that a 

 permanent deflection of 1 mm. corresponded to a current of 2 X 10-" 

 Amp., showed, wiien a current was suddenly passed or interrupted, 

 (see figure 2 in the text) a number of oscillations. B}- inserting a 

 capacity c = 0.135 ft/' the motion was damped to such an extent 

 that the limit of aperiodicity was reached. Next the tension of the 

 striuff Avas exactly 4 times relaxed so that a deflection of 1 mm. 

 was caused r)y 5 X 10-^ Amp. The oscillations then re-appeared, 

 and could not be checked again until the capacity was increased to 

 0.40 (if. With a 4 times suialler tension, i.e. with a 4 times greater 

 sensitiveness the capacity and at the same time the value of 7' had 



