174 Scientific Proceedings, Royal Dublin Society. 



those of the condenser, a leyden jar of about 90 cms. capacity. Connexions 

 were made from the condenser-terminals by means of wet thread to the 

 Kelvin electrostatic voltmeter. The wet tliread possessed a very high resis- 

 tance, and was employed with a view to testing whether the condenser was 

 actually charged to a steady potential, or if, on the contrary, its potential was 

 alternating. By allowing the flames to vibrate under the influence of the 

 a.c. alone (polarizing current cut off), that is to say, when the condenser- 

 potential was alternating, it was found that the voltmeter reading was zero. 

 On polarizing the magnets, the voltmeter immediately charged up, and showed 

 a potential about the same as that registered when connected directly to the 

 coil. If the insulation of the condenser and voltmeter had been better than 

 they were, we should have expected to obtain perhaps a slightly higher 

 potential, corresponding to the peak value of the high-tension e.m.f. 



A somewhat more convincing demonstration of the rectifying property of 

 the device was achieved by using a Braun cathode ray-tube as an oscillo- 

 graph. A small coil was mounted near the cathode stream, and formed part 

 of the high-tension circuit. With the rectifier functioning, two spots were 

 formed on the fluorescent screen, one being due to the undeflected rays. The 

 other spot was, of course, produced by rays deflected by the intermittent 

 rectified current, and was several centimetres from the former. No third 

 spot was visible, nor was the undeflected spot even noticeably widened on the 

 side remote from the second spot. With the cutting off of the polarizing 

 current, there was produced a band of fluorescence to each side of the centre 

 spot, the contrast between the two conditions being very remarkable. 



It was hoped to apply the device in conjunction with a mercury break- 

 interrupter, but work in this connexion has been postponed for want of 

 leisure. In a preliminary trial of such an arrangement one interesting fact 

 came to our notice. It is probable that a single flame will not act as an 

 efficient rectifier with much higher voltages than those we used, since the 

 flame is strongly acted on by intense electrostatic fields, and cannot be made 

 to vibrate regularly in the spark-gap. Besides, the gap has to be of consider- 

 able width, and it seems clear that several flames side by side (all vibrating 

 in synchronism) will be necessary in such cases. There should be no great 

 difficulty in devising an arrangement of this kind, 



SUMMAKY. 

 High-tension a.c. current can be rectified by interposing in the circuit one 

 or more spark-gaps, in which the conductivity is altered in synchronism with 

 the e.m.f. by means of a vibrating flame. Apparatus acting on this principle 

 is described, and an account given of some tests of its operation. 



