AN OSCILLOGRAPH FOR TEN THOUSAND CYCLES 



81 



It is possible, of course, to shorten the string and to employ a shorter 

 pole face. Halving the string length might be expected to double the 

 natural frequency, although it would reduce the sensitivity to one 

 quarter its former value. The linearity between deflection and cur- 

 rent, however, holds only so long as the deflection is small enough not 



4000 6000 8000 10,000 



FREQUENCY IN CYCLES PER SECOND 



14,000 



Fig. 7 — Equalizing network employed with new oscillograph and the characteristic 



obtained. 



to increase the tension appreciably, so that the shorter the string the 

 less is the permissible deflection. To compensate for this and return 

 to the original size of oscillogram requires an increase in optical mag- 

 nification, which in turn reduces the transmitted light and thus the 

 speed at which the paper can be exposed. It also increases the width 

 of the string image, which thus becomes a larger proportion of the 

 total deflection, but there is a compensation in that the sensitivity 

 is somewhat increased. Such a design, although capable of responding 

 to a higher frequency, and having a sensitivity greater than that which 

 would be obtained from the shortened string without the additional 

 optical magnification, is less capable of making a photographic record. 

 Actually, with a given string material, light source, and magnetic field 

 strength, there is a definite length of string that will give the widest 

 frequency range both electrically and photographically. It turns out 

 that by using the longer string and the methods of equalization already 

 discussed, the overall sensitivity is about the same as that for the 

 shortened string, and that the optical disadvantages are avoided. 



