( 110 ) 



In fig. 3 plate I a movement of the string is represented when 

 a cnrreiit of 3 X iO~^ Amp. is suddenly made and broken. The 

 sensitive plate has been moved along with a tenfold velocity and the 

 string has ten times more tension than in fig. 1, consequently one 

 mm. absc. = 0.01 second and one mm. ord. = 10-^ Amp. The gal- 

 vanometer circuit contains again one Megohm so that the same causes 

 of damping exist as in fig. 1. The movement is still dead-beat, but 

 on account of the 10 times greater force on the string it is 10 times 

 quicker, as can easily be ascertained by comparing the great descending 

 curve of tig. 1 with one of the curves of fig. 3 or better still by 

 supei-posing diapositives of the curves of both figures. They will 

 then be seen to cover each other exactly and since in one figure 

 the velocity of the moving plate is ten times greater than in the 

 other, the deflection of the siring must in one case take place ten 

 times more quickly than in the other. At the same time the resistance 

 of the air is proved in our case to increase proportionally to the 

 velocity of the string itself. 



In recording the curves of fig. 4 and 5 of plate I the velocity of 

 the moving plate has been increased to 250 mm. per sec. so that 



1 mm. of the abscissae is 0.004 sec. The plate at first moves slowly 

 and reaches the mentioned velocity only when it has travelled through 

 a distance of 4 or 5 centimetres, whereas the spokes of the rotating 

 disc always cast their shadows on tlie plate accurately every 0.004 

 second. Hence the coordinate system is in the first sixth part of the 

 photogram compressed in the direction of the abscissae. 



In fig. 4 one mm. ord. = 2X10~^-A.mp., while in fig. 5 one mm. 

 ord. = 3X^0^^ Amp. These two figures together show us the limit- 

 value of the sensitiveness for which the movement of the string is 

 still dead-beat. In fig. 4 a current of 4X^0^" Amp., in fig. 5 a current 

 of 6X10-" Amp. has been transmitted through the galvanometer and 

 interrupted. One sees that the deflection in fig. 4 is still dead-beat 

 and is completed in about 0.009 sec, whereas in fig. 5 the motion 

 begins to become oscillatory and for a single oscillation takes 0.006 

 sec. The sensitixeness wdth w^hich the motion of the string is on the 

 border between aperiodic and oscillatory motion is consequently such 

 that a deflection of one millimetre corresponds to a current between 



2 and 3 X l^-» Amp. 



In the tracing of fig. 4 and 5 only an insignificant resistance is 

 put into the galvanometer circuit so that here besides the viscosity 

 of the air also the ordinary electromagnetic damping checks the motion. 



Now^ some particulars may be mentioned referring to the 5 photo- 

 grams of plate 1 in common. 



