( 218 ) 



Finally we mention still two series of measurements with a still 

 thinner string, n" 14. 



In the first photogram we tind with F = 500, and c = 5,75 that Tis 1, 

 and ^==3,8 from which is calculated m = 3,7 X 1^~^ [^>">^ — M]- 



In the second photogram V is unchanged but c = 3,15, T^ 0,705 

 and k = 3,16. 



From this we calculate ??i = 3,5 X 10~^ [?«?>i — iiA]. So we may 

 take for the mass of string n° 14 the mean value which is 

 m = 3,6 X 10-3 [-„^„^ _ jt^4j, 



4. The resistance to the motion of the string. 



The resistance to the motion of the string can be determined in 

 various ways. We shall begin with a description of the method which 

 may be considered to give the most accurate results. 



Let the quartz thread be only moderately stretched, and let it 

 suddenly be passed by a current of constant intensity. Let the 

 deflection of the thread be recorded on a rapidly moved sensitive 

 plate, so that a curve is obtained, which is schematically represented 

 in the followino; fi2:ure 1. 



Pig. 1. 



From A io B the quartz thread is in the 0-position. At B the 

 constant current is made, by which the image of the string is moved 

 upward until it reaches its second position of equilibrium about Z). 



