1905.] on a Pertinacious Current. 81 



a current generated by mechanical and magnetic means, to convert 

 it into an intermittent current at very high pressure, and then to 

 store the quantity thus propelled, in reservoirs supplied with valves 

 which prevent the flow back ; so that the whole quantity transmitted 

 in successive impulses accumulates, until the reservoir becomes full 

 and overfull, so that it overflows, giving a steady stream or trickle 

 through great resistances, and maintaining the continuous high- 

 tension current required. It is as if a reservoir were being charged 

 by a water-ram, or by waves which splash up into it through a hole, 

 the hole being provided with a valve whereby the water supplied is 

 trapped and not allowed to flow back again each time in futile 

 manner, but is kept stored and accumulated until the pressure has 

 increased to an enormous extent : the process is, in fact, exactly 

 like pumping air through a valve into a closed reservoir, by inter- 

 mittent strokes of a pump, and then allowing the reservoir to leak 

 through a small hole, as soon as the pressure has become sufficient. 



On the plan customarily used for obtaining Leyden-jar sparks in 

 spectrum analysis, etc., the jar is charged at every break of the coil, 

 but the charge immediately subsides through the wire of the coil, 

 and so the jar is perfectly empty in a minute fraction of a second 

 after the discharging impulse ; accordingly unless the overflow spark 

 occurs instantaneously it will not occur at alL There is no accumu- 

 lation of impulses, and only a short spark can be obtained. But 

 when a valve is inserted, then the charges do not sink back through 

 the generating coil, but accumulate, and the overflow spark length 

 now may be very much greater. 



The chief use to which I wished to apply this arrangement was 

 to the dissipation of fog or smoke, or the deposition of metallic fume, 

 and the principle of that application is shown by attaching to the jar 

 a wire which leads to a point immersed in some fog or smoke in a 

 bell jar or other vessel ; and now, by a momentary excitation of the 

 coil, the jar or reservoir is filled up to bursting-point with electricity, 

 which at this high pressure continues to discharge or fizz from the 

 point for some time, say ten seconds or thereabouts, by which time the 

 fog has completely disappeared. 



In order to fill a vessel with an atmosphere of fog or smoke, 

 almost any plan serves ; one way is to burn smouldering brown paper, 

 but that is not at all a good plan, since the smoke is not dense, and 

 being hot it hovers about at the top ; another is to burn tobacco, 

 which does better : in fact, very fairly well ; another plan is to burn 

 magnesium wire, which is a cleanly and good method, and the smoke 

 being sohd and white, it illustrates the process of dissipation very 

 well ; another is to make a chemical smoke by the use of hydro- 

 chloric acid and ammonia, or by burning sulphur in an ammonia 

 atmosphere ; indeed, there are plenty of plans known to chemists ; 

 but the method I prefer for the present purpose is to make arti- 

 ficially a mist or fog of water vapour. It may, for instance, be 

 Vol. XYIII. (No. 99) g 



