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sensitiveness has been diminished to c = 100 and hence the tension 

 is over 300 times the proper weight of the thread. 



We must not lose sight of the fact that besides the stretching 

 arrangement tliere are various forces which act on the quartz thread. 

 If the thread is so thin that its elasti(*ity may be neglected while 

 only gravity has to be reckoned with, it will assume, when entirely 

 relaxed, the shape of a catenary. If it is paramagnetic it will be 

 bent towards one of the poles in the strong magnetic iield which is 

 never perfectly homogeneous. And if its elasticity may not be 

 neglected, it will assume shapes, determined by the position and the 

 direction of the extremities at the places of attachment, while also 

 a slight torsion about the longitudinal axis may make itself felt. 



When the tension of the thread is gradually increased by screwing 

 the upper end of the thread upwards, it is easy to observe with the 

 microscope the moment at wliicli the thread is pulled straight. 



Before the thread is straight its middle will be displaced nearly 

 in a horizontal plane when the stretching arrangement is screwed 

 up. After the thread has been pulled straight the middle is displaced 

 upwards on account of the elongation of the thread, this displacement 

 being half that of the extremity of the thread. The thread once having 

 been pulled straight, already a small increase in tension will force 

 it to move like a stretched string. 



The results of the calculation about the tension of the quartz thread 

 are in agreement with the relation existing between this latter and 

 the distance of the two extremities of the thread. Of most of the 

 quartz threads it might be assumed that they were just on the verge 

 of being stretched when their sensitiveness corresponded to about 

 1 mm. deflection for '10^^ Amp., or c = 100. In this position very 

 small changes in the mutual distance of the extremities cause already 

 great differences in the sensitiveness. But when the mutual distance 

 of the extremities has once been so far shortened or lengthened that 

 the sensitiveness has thereb}^ become either considerably increased, 

 e. g. to 1 mm. deflection for 10— ^"^ Amp, or considerably reduced, 

 e. g. to 1 mm. deflection for 10~^ Amp., conditions are altered. Then 

 great displacements can be given to the upper end of the quartz 

 thread by means of the stretching arrangement, causing only relatively 

 small changes in sensitiveness. 



Further the sensitiveness of the thread, once stretched, shows an 

 increase which is inversely proportional to the increase in length. 

 So e. g. with string n". 13 the sensitiveness will be diminished for 

 an extension of 100 (x from c = 100 to c = 10, and for another 

 100 ft from c = 10 to c := 5. The sensitiveness is inversely proportional 



