241 



diameter and 10 cm. leiigtli with a microscopic magnification of 

 1000 times. The next column shows the strenglii of the field H in 

 Gauss, and the hxst cohimn contains once more the frequencies. 



Gold fibres, if critically damped, will give a larger deflection than 

 strings of any other material, but of the same dimensions. The time 

 of vibration, and consequently the time of deflection is larger than 

 with other strings. Hence we cannot easily compare the results 

 This table is only useful if we wish to calculate the possible 

 deflection with strings of other dimensions. In order to get compar- 

 able figures we shall have to consider strings of the same diameter, 

 which have the same vibration time. A formula for this case can 

 be given by calculating 



h 

 iw 



1 



1 



A^=5400— . — ^z=: (16) 



This formula represents the deflection caused by 10 Volts through 

 a string of a diameter d, completely relaxed, and vibrating once a 

 second, whilst placed in a magnetic field of a strength, sufficient to 

 cause the movement of the string to be entirely damped. In this 

 case the length is predetermined for any material by the condition 

 that the frequency is one per second. 



In table IV we give a few figures which can be calculated by 

 this last formula. 



TABLE IV. 



w 



Deflection per (iV. with d =1^. 

 and V= 1000 X 



241 mm 

 245 „ 

 188 „ 

 276 „ 

 73 « 



From this table we see that aluminium is the best material for 

 strings in an Einthoven galvanometer if used for the measuring 

 of small potential differences. A stiing of 1 [i, completely relaxed 

 and 6.65 cm in length, gives vibrations of one second. With it we 

 can get a deflection of 276 mm for 1 microvolt, if the field be 

 adjusted at 997 Gausses; and the microscopic magnification amounts 



16 



Proceedings Royal Acad. Amsterdam. Vol. XXI. 



