( 225 ) 



for string 10 without silver 2,4 ji, silvered 3,0 f* 

 ,, ,, lo ,, ,, l.bft, ,, 2.5 fx 



,, ,, 141: ,, ,, l.i II, ,, l.iJ [Jy 



We leave unsettled what function the air-damping is of the diameter 

 of the string, but wish to point out here particularly the influence 

 which the damping maj experience from the layer of silver on the 

 quartz threads being more or less smooth. Especially string 14 has 

 an almost perfectly smooth coat of silver, while the skin of string 

 10 shows distinctly visible inequalities. 



We will now investigate whether the amount of Va for a delinite 

 string may be regarded as constant, however much the tension of 

 the quartz thread and thereby the velocity^ of its deflections may 

 be modified. 



For this it is necessary to measure ?'« once more with a strongly 

 stretched string and oscillating deflections, but the methods which 

 are at our disposal for this purpose do not nearly furnish such 

 accurate results as could be given above. We mention here two 

 methods of measuring. 



In the first place the same method as above may be used, but 

 this time it is applied under unfavourable conditions. As the string- 

 makes rapid movements, the tangent of the angle of inclination 

 becomes large, so that its amount cannot be determined with the 

 desired accuracy. Besides the uncertainty in the value of q also 

 increases very much. 



Of the curves, by means of which in the preceding chapter the 

 mass of the string was calculated, plate A 61 of string 13 shows 

 the greatest value of 2\ viz. T=l,32 mm. I therefore have chosen 

 this curve for an attempt to determine the value of /■ by formula (15) 



._ 9 

 cvd 

 A resistance of more than 1 Megohm was inserted in the galvano- 

 meter circuit so that the electromagnetic damping might l}e neglected 

 and consequently r might be put = Va- The following- values 

 were found : 



g=9 niM. 



c = 5,69 mM. per micrampere. 



V = 88,1 



f/= 0.979. 



As the quartz thi-ead with rapid motion writes a fine line on the 

 sensitive plate, the angles of inclination can be measured with great 



16 



Proceedings Royal Acad. Arasterdam. Vol. VIII. 



