( 226 ) 



accuracy. An error of 0,1" is possible, however, in the measured 

 value of the angle. And if the real angle is 0,1° gi-eater than the 

 value found, the tangent must be taken 104,2 instead of 88,1. So 

 an error of 0,1° in the measurement would cause here an error of 

 over 18 7,, hi the linal resull. Putting the uncertainty in the value 

 of ([ at 1,5 mm., also the probable error, caused by this alone, is 

 found to be 17 7„. 



The measuring arrangement which we used, does not enable us 

 to make the result more correct. 



In the second method of determining the value of the resistance 

 to the motion of the string with a strongly stretched, oscillating 

 string, we make use of the following formula: ^) 



rT 

 l,ink = — (16) 



4:1/1 



in which the letters have the same meaning as before, viz. 

 k = the damping ratio, 

 /• = the resistance sought, 

 7'= the period of the oscillatory deflections, 

 m = the mass of the string. 

 We write formula (16) in the foj-ni : 



4 m Ian k 

 »- = -^ (17) 



and substitute for m the value which we found, according to formula 

 (7) of the preceding chapter, to be 



2':. 



We then find 



c {39.5+4 (VAf 

 4 T Ign k 



(7) 



(18) 



o|39,5+4(/^/?Af| 



In order to obtain comparable results, we always calculate r for 

 a speed of the sliding frame F=: 500 mm. per second, using again 



fornuda (14) /;, = /v. ~ • 



From the two last mentioned formulae the value of ;■ is now 

 calculated for four out of the fixe curves which in the preceding 

 chapter served for the deterniinatio]i of in. Duiiug the recording of 

 these curves a great resistance of more than 1 Megoiim was each 

 time inserted in the gahaiiometcr circuit, so that the resistance to 



1) Vide e.g. Kohlrausch 1. c. p. 448. 



