172 



Scientific Proceedings, Royal Dublin Society. 



upper branch of the hysteresis curve. The most favourable vak;e for this 

 " polarizing " current is best got by trial, the manometric flame being observed 

 in a rotary mirror, and the " polarizing " current gradrially increased until the 

 alternate maxima of the flame are seen to disappear. A little adjustment of 

 the relative positions of the magnet and capsule may be required to obtain 

 the largest amplitude in the flame-vibration. The dimensions of the capsule 

 and jet are also very important in this connexion, the best results being 

 obtained vyhen the capsule is rather shallow, so that considerable changes in 

 its volume, and therefore in the gas pressure, result fi'om the movements of 

 the membrane in and out. A jet should be selected such that the flame will 



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be about eight or ten centimetres high, while the supply-tube leading the gas 

 into the capsule should either be of narrow bore or lightly plugged with cotton 

 wool where it opens into the interior of the capsule. With a capsule of 2 c.c. 

 volume and a jet-tube of about 1 c.c, making about 3 c.c. in alt, the rubber 

 diaphragm being about 3 cms. in diameter, we obtain flames oscillating between 

 1 cm. and 10 cms., the height when not vibrating being about 9 cms. 



The application of the device for the purpose of rectifying was tested as 

 follows: — A large (Newton) induction-coil was employed to transform the ordi- 

 nary town a.c. supply (200 volt, 50 -.) to about 6,000 volts. In the secondary 

 circuit, as well as the rectifying spark-gap^ cc, were included a small 

 vacuum tube and a d.c. milammeter. The vacuum tube was placed in such a 

 position that the reflected image of it in a fixed mirror was vertically beneath 



1 The flat ends of two stout carbon rods were found most satisfactory fortius, 



