707 



had been made in the application of the metliod, so that we must 



consider as a failure this part of our investigation. The negative 



sign of the circulating electrons is however made very probable by 



the agreement between the magnitude of the observed effect and 



e 

 the value we have deduced for it from that of the ratio - for 



m 



negative electrons. 



§ 7. Move accurate measurements. 



The measurements thus far described furnished a satisfactory con- 

 firmation of the theory, but were much lacking in precision. The 

 field in the coil was too weak practically to cause the sudden 

 reversals of the magnetisation assumed in tiie theory. Further the 

 coefficient of damping ;: could not be detei-mined with any accuracy. 

 Even the question may aiise whether the iuliuence of the tlaniping 

 is represented rightly by tiie term P(t in equation (6). 



For these reasons we have somewhat modified our apparatus. In 

 order to quicken the reversals of the magnetisation we used instead 

 of the former siiort coil one of 62 cm length (about 100 windings 

 to a cm) the amplitude of whose field, for an effective strength of 

 1,45 Ampère was 2(50 Gauss in its central part and therefore 130 

 Gauss at the ends. In order to diminish the demagnetizing infiuence 

 of the poles we further used a cylinder of 16 cm length and 0,17 cm 

 diameter. The mirror was now suspended by a thin walled tube that was 

 sealed to the lower end of the iron cylinder. It just projected beneath 

 the lower end of the coil. In order to avoid a determination of the 

 coefficient of damping and assumptions about the law of damping 

 a series of experiments were made in which, for a definite length 

 of the wire, the amplitude \<(\ was determined for different frequen- 

 cies of the alternating current, so that a "resonaiu-e curve" could 

 be drawn. 



The alternating current was furnished by a generator placed in 

 the cellar of the building and moved by the current of a battery 

 of storage cells. The apparatus in the working room comprised a 

 variable resistance connected in parallel to the windings of the field 

 magnets. By varying this resistance we could change within certain 

 limits the exciting current in the motor and therefore the number 

 of its revolutions and the frequency of the induced alternating 

 current. The current which passed through the variable resistance 

 was controlled by an ampèremeter. When all other things were kept 

 constant the frequency of the alternating current was a function of 



