586 SECTIONAL TRANSACTIONS.— G. 



the problem. Further a simple a.c. to d.c. converter is already to hand in the mercury 

 arc rectifier, if this can be used for such high frequencies. If, then, these two can 

 be combined, transmission by induction, coupled with ordinary d.c. traction motors, 

 becomes possible. For the past four years various research students have been at 

 work at Birmingham on the parts of this combination, with the object of finding 

 answers to the following main questions : 



1. Can an overhead system of the type proposed act as an efficient power trans- 

 former ? 



2. Can the Poulsen arc be developed into an eflGicient generator for these purposes ? 



3. Will an arc rectifier operate at frequencies of 20,000 and upwards ? 



The progress of the work is reported in this paper, and may be summarised as 

 follows : 



1. The efficiency of transformation is very good. 



2. The primary should be supplied with constant current at varying voltage, under 

 which conditions the Poulsen arc operates very well. The overall efficiency can 

 probably be made satisfactory by a suitable choice of voltage and current. Reliability 

 and steadiness are not so certain, and more work is necessary in this direction. 



3. The arc rectifier will function quite satisfactorilj^ even up to 107,000 p.p.s., 

 but some further work is necessary upon the regular maintenance of the arc. 



The whole combination, consisting of Poulsen arc, transformer, mercury arc and 

 motor, has operated in the laboratories at 75,000 p.p.s. without difficulties other 

 than those referred to above. The thanks of the University are due to the Department 

 of Scientific and Industrial Research for the help that has been accorded, and to the 

 Royal Society for a contribution towards the cost of the apparatus. 



Mr. B. Hague. — Experimental Methods for determining the Distribution of 

 Electric and Magnetic Fields. 



Dr. J. Hartmann. — The Jet-Wave and its Applications. 



A conductive liquid jet, preferably a mercury jet, passes a constant magnetic field 

 the Hnes of force of which are perpendicular to the jet. The latter touches a special 

 electrode, which does not deform the jet appreciably. Through the said electrode 

 and the jet-producing nozzle an electric current may be transmitted into and out of 

 the jet. The interaction between the current and the constant field will transform 

 the jet into a so-called jet-wave, the shape of which depends on the character of the 

 current used in the production of the wave. 



If the current is uni-directional a simple bend is produced. The latter travels 

 forward with the velocity of the original jet, the separate particles of the wave-bend 

 radiating from the centre of the field along straight lines. The height of the bend 

 thus increases proportionally with the distance from the field. On this type of waves 

 the so-called jet-wave interruptors for the operation of X-ray inductors are based. The 

 jet is inserted in the primary circuit of the inductor. The current growing up in the 

 said circuit will create a wave as described. In travelling forward the wave will hit 

 a knife mounted between the field and the electrode, through which the current is 

 led into the jet. The knife will cut the wave, thereby interrupting the circuit, which 

 is not closed again till the front of a new undeflected jet has arrived at the electrode 

 from the field. It will be understood that the wave just considered may also be 

 employed as a member of simple relays and regulators. A characteristic of the jet-wave- 

 relays and regulators is their definiteness of operation. 



With a simple alternating current through the jet a continuous train of regular 

 waves is created. Approximately the waves have the shape of a sine-curve with 

 steadily increasing amplitude. On this wave the synchronous jet-wave commutator is 

 based. In the latter the wave is directed against a twin electrode consisting of two 

 steel bars with a gap between and a knife arranged just above the gap. Above the 

 twin electrode is arranged an electrode, the tapping-electrode, which is in unbroken 

 contact with the wave during its motion. Obviously the wave will alternately for 

 half a period of the current used in the production of the wave connect the tapping- 

 electrode with the two components of the twin electrode. Consequently the device 

 may be used for rectification of any alternating voltage synchronous with the wave- 

 producing current. It forms the main member of the jet-wave rectifier, presumably 



