300 Mr Aston, Neon Lamps for Stroboscopic Work 



Neon Lamps for Stroboscopic Work. By F. W, Aston, M.A., 

 Trinity College (D.Sc, Birmingham), Clerk-Maxwell Student of 

 the University of Cambridge. 



[Read 19 May 1919.] 



For the accurate graduation and testing of revolution indicators 

 and similar technical purposes the stroboscopic method is probably 

 the most reliable. This depends on the fact that if a rotating disc is 

 illuminated N times per second by very short flashes, a regular 

 figure drawn symmetrically on the disc will appear at rest when 

 the number of revolutions of the disc per second is some exact 

 multiple or submultiple of N depending on the number of sides of 

 the regular figure. 



The value of N — in practice 50 — can be s^t and easily kept 

 extremely constant by the use of an electrically driven tuning-fork 

 so that the success of the method rests principally upon the 

 illuminating flashes ; its accuracy will depend upon their shortness 

 of duration and brightness; its convenience as a practical method 

 upon their brightness and quality as affecting the eye of the 

 observer. 



The first experiments were tried with naked Ley den jar sparks 

 obtained from the secondary of an ordinary ignition coil, the 

 tuning-fork being introduced into the primary circuit as an 

 interrupter. These showed the principle of the method to be 

 excellent but spark illumination left much to be desired; it was 

 noisy, feeble in intensity, and being mostly of short wave-length, 

 caused rapid and excessive eye-strain even when used in a dark 

 room. 



The remarkable properties of Neon seemed to offer an almost 

 ideal solution of the illumination problem. A form of lamp to 

 replace the spark was therefore devised which appeared likely to 

 give good results and several of these were filled from the author's 

 stock of Neon at the Cavendish Laboratory. The success of these 

 lamps was immediate, eye-strain disappearing completely. The 

 present paper is a description of the lamps and their behaviour 

 during continuous use. 



The Form of Lamp. 



The original form of the lamp, which it has not been found 

 necessary to alter materially, is shown in the sketch. As, in the 

 discharge in Neon, nearly all the light is in the "Positive Column" 

 and its brightness increases with the current density, the lamp 

 was designed to give a positive column as long and narrow as 



