Physiology. — "llie string galvmiometer in wireless telegrai^hy" . 

 By W. F. EiNTHOVEN. (Coinmiinicaled by Prof. W. Einthoven). 



(Communicated at the meeting of Marcli 24, 1923). 



The string galvanometer, as is well known, consists of a conduct- 

 ing fibre stretched like a string in a strong magnetic field. A cur- 

 rent passing Ihrongh the fibre indnces a displacement of it in a 

 plane perpenilicniar ^lo the lines of magnetic force. The deflection 

 can be observed with a microscope and the magnified image can 

 be photographed. 



Many attempts have been made to use this instrument for the 

 reception of wireless .signals, bnl only ordinary models, with a 

 relatively long, not very mnch stretched sli-ing have been tried, and 

 tliese show great sensitiveness towards disturbing direct cnri'enls. 

 The wireless signals were received in such a way that the high 

 frequency oscillations were rectified by means of some device, and 

 the rectified current impnlses were passed thiongh the string; this 

 was affected in the same way as when conveying a true direct 

 current. 



But, used ill this way, the string galvanometer has only brouglit 

 disappointment in wireless telegraphy, for it reacts to every current 

 of some duration with the same sensitiveness, and even the smallest 

 atmospherics are sufficient to give trouble. Some large Companies, 

 who have tried to nse the string galvanometer at their transatlantic 

 stations, have abandoned work with it. 



The application here to be described of the instrument is based 

 on a quite different method '). The incoming high frequency oscil- 

 lations are not rectified but are sent through the string immediately. 

 The string is short and stretched so much, that its own period 

 corresponds to the period of tiie ether waves used in wireless sig- 

 nalling. Choosing the lenght of the string conveniently and adjusting 

 its tension, we can bring it in tune with |)ractically all continuous 

 waves available in radio-telegraphy. If for instance these ha^e a 

 length of 1 kilometer corresponding to 300.000 periods per sec, the 

 string is adjusted so that the proper frequency of its vibrations is 

 also 300.000 per sec. 



1) Patented. 



