( 224 ) 



ordinates must be considered as perfectly equal. More accurate 

 measurements have already been mentioned in the preceding chapter 

 and need not be discussed again. 



From the table follows that in the examined photogram 1 scale 

 division along an absciss = 0.9675 mm. Since the length of a scale 

 division along an ordinate has already been given in millimetres we 

 can directly express a scale division along an absciss in scale divisions 

 along an ordinate. Calling this value d, we find in photogram A 34 

 d = 0,964. In other photograms we found values for d, varying 

 between 1,033 and 0,901. 



If d deviates somewhat considerably from unity, the value of the 

 tangent of the angle of inclination will have to be corrected. If the 

 tangent of the measured angle of inclination is v, we shall have to 

 take the product vd instead of v in the computation of r. 



Formula (13) is then replaced by 



cvd 



(15) 



We now give some results of measurements, for convenience' sake 

 assembled in the following table III. 



TABLE III. 



During the recording of the curves to which the numbers of this 

 table refer, always a great resistance — more than 1 Megohm — 

 was inserted in the galvanometer circuit, so that the electromagnetic 

 damping might be neglected and the resistance Va to the motion of 

 the string was only caused by the air. We see that the value of 

 ?^a, which for all the curves has been calculated for Fm 500, 

 decreases in the order of the numbers 10, 13 and 14 of the quartz 

 threads. In the same order also the thickness of the silvered strings 

 diminishes. The diameter is ; 



