22 Overhead Electrical Discharges. [april, 



spark will leap over a graduated spark gap, the whole matter 

 should take but a very small proportion of time. 



Occasional overhauling of the apparatus from time to time 

 by an expert electrician seems to me, from my experience 

 with the Bitton apparatus, a very desirable precaution, as 

 otherwise valves are likely to be overstrained and conse- 

 quently finally break down. 



Presumably, however, the tendency will be, with time and 

 more experience, to render the apparatus more and more 

 what the modern motor-car is sometimes described as being, 

 viz., 44 fool-proof," or, in other words, capable of complete 

 control by non-experts. 



By means of the high-tension apparatus the current is raised 

 to a very high voltage; something like 100,000 volts is the 

 usual figure, and now great precautions have to be taken to pre- 

 vent unintended leakage and consequently, such a decrease in 

 the voltage that the current no longer discharges upon the 

 proper area. To avoid this the current is carried by thick 

 telegraph wire— the thicker the wire the less the chance of 

 leakage into the air — borne upon insulators raised some 

 16 feet above the ground by means of larch poles, the poles 

 being planted firmly, when possible by the hedges, but of 

 necessity in large fields, some in the open field. 



By judicious arrangement the network of wire necessary 

 to charge twenty acres can be carried by some 20 poles. 

 The insulators have to be of a special type to prevent as far 

 as possible leakage down the pole, which is likely to occur 

 in spite of the fact that the charged wire never touches the 

 insulator or pole, but is fastened to it through the agency of 

 yet another insulator and a short piece of wire. 



Serious leakage in wet weather and for some hours subse- 

 quent to rain can probably never be prevented, but it is 

 certain that, with the devices now adopted by Mr. Newman 

 and with a new form of insulator now in use at Evesham, 

 given dry conditions, the discharge takes place from the 

 part of the overhead system intended for the purpose. This 

 discharge area consists simply of a series of thinner wires 

 stretched taut between two of the parallel thick wires. With 

 lower voltage it would probably be necessary to supply 

 downwardly directed points at intervals along the discharge 



