( 249 ) 



yet llic niolion of llio (|nar(/. llii'oad as a wliole lias a more com- 

 plicated cluxracler. 



Calling' 7??i the i-eal mass of the string in grammes, 2\ the period 

 in seconds and c^ the sensitiveness in centimetres deflection of the 

 middle of the string per dyne, we have 



m,=.nx{j)X-X-^ .... (20) 



The factor— is introduced by the circumstance we mentioned 



8 



already above. The method by which the amount of this factor is 

 calculated will be given later, after the tension of the string will 

 have been dealt with. We now proceed to a nearer discussion of 



the values of -7 and — . 



T represents the time in millimetres while the velocity of motion 

 of the sliding frame is T^ mm per second. The time in seconds is 

 coiisequently 



T 



or 



1\ 1 



(30) 



c 

 In order to determine the value of — , we must take into account 



the magnitication used, h, the strength of the magnetic held H and 

 the length of the string /. 



H is expressed in (C.G.S.) units and / in centimetres. 



c, as was mentioned before, is the sensitiveness, expressed in 

 millimetres deflection of the image of the string per micrampere, 

 Cj being the sensitiveness, expressed in centimetres deflection of the 

 middle of the string itself per dyne. 



The force deflecting the quartz thread ^vllen a current of 1 micram- 



pere is passed, is -— dynes. Hence 



HI 



or 



c Hlh 



v = w <-''^ 



By means of the formulae (29), (30) and (31) we can now express 

 m^ in m and find : 



