( 267 ) 



among' the tln-eo (lircads nieiilioued, ii". 14 will luxvc to bo preferred, 

 since the amount of the normal sensitiveness as well as the resistance 

 of this thread exceed those of the two other threads. 



Finally we make some remarks as to the maimer in wiiich the 

 velocity of deflection may be raised to a maximum. A great velocity 

 is in general obtained at the expense of the sensitiveness. But there 

 are a number of investigations, notably the recording of sounds, ^) 

 in which the sensitiveness of the string galvanometer may be very 

 considerably diminished. Even when the string, at the risk of break- 

 ing, is stretched to its maximum and hence its sensitiveness reduced 

 to a minimum, relatively' feeble sounds can still drive the image of 

 the string out of the field of vision. 



By strongly stretching string 14 we could impart to it an oscil- 

 latory motion of which the period was T= 1,41 ö". If the oscillations 

 were damped by means of the condenser method, a deflection could 

 be obtained, requiring a time of 0,8 a and proportional to the 

 current to be measured with an error of 3 7o ^}- If '^^^ accuracy ot 

 0,3 ° „ was desired, one had to be contented with a time of deflec- 

 tion of 2,2 Ö. The sensitiveness was here 1 mm deflection for 

 3 X 1Ö-' amp. 



From the data of the preceding chapter follows that under these 

 conditions the tension of string 14 can be still 3 times increased 

 befoi'e its breaking point is reached. Hence if the string is so strongly 

 stretched that it is at the point of breaking, its deflections will become 

 1/3 times quicker, so that its oscillations will show a period T =z 

 0,815 fj. In practice we have not raised the tensioji of string 14 so 

 high, however. 



The question how to obtain quicker oscillations was simply solved 

 by nsing a shorter wire. String 20, wliicli was already discussed 

 abo\'e, has a diameter of 1 ft and is 25 mm long. With a practi- 

 cable tension that could be applied without risk of breaking, it 

 performed with a sensitiveness of 1 nnii deflection for lO^^ amp, 

 oscillations of a period of 0,3J 6. 



This period corresponds to a tone of 3230 vibrations per second, 

 about ƒ/'* sharp or almost the highest tone of an ordinary j)iano. 

 We remark that the string can still be shortened and l)c more 

 strongl}' stretched, so that a much higher jiumber of vibi-atious can 

 easily be reached, while it must also be borne in mind that a string 

 with slow deflection can yet very accurately record sound vibrations 



1) On the motliod of recording sounds see these "Proceedings" G p. 707, 1904, 



2) See these" "Proceedings" 7, p. 315, 1904. 



