. Induction coils : how to make, use, and repair them including Ruhmkorff, Tesla, and medical coils, Roentgen radiography, wireless telegraphy, and practical information on primary and secondary battery . om point to point. If two small metal balls be substituted(Fig. 35) for the points between which thesparks be passing, it will be noted that thesparks do not pass through so great an airgap as before, or even as rapidly. The spark between two balls is muchnoisier than that passing between points,and if the balls be of about i inch in Experiments. 25 diameter, a curious effect ensues on thepas
. Induction coils : how to make, use, and repair them including Ruhmkorff, Tesla, and medical coils, Roentgen radiography, wireless telegraphy, and practical information on primary and secondary battery . om point to point. If two small metal balls be substituted(Fig. 35) for the points between which thesparks be passing, it will be noted that thesparks do not pass through so great an airgap as before, or even as rapidly. The spark between two balls is muchnoisier than that passing between points,and if the balls be of about i inch in Experiments. 25 diameter, a curious effect ensues on thepassage of the current (Fig. 36). This Fig. 35. Fig. 36. effect has been likened to a stream ofwater issuing from a horizontal nozzle intoa cavity when the nozzle is moved up anddown slowly in the space of a few inches. The Luminous Pane. This easily made exhibit (Fig. 37) is onethat is susceptible of quite a nuQiber of ap-plications. In its simpleform it is but an enlargedversion of the rubbersheet scattered with car-bon dust. The old wayto make it was to takea plate of glass and ce-ment on one face of it a sheet of tinfoil,using shellac varnish preferably. Whendry, the tinfoil was scored across and. Fig. 37. 126 Experhnents. across in such manner as to divide it upinto little squares or diamonds. Whenthe current was applied to each end of theplate, the spark divided into innumerablelittle ones ; between each bit of tinfoil andits neighbors there would be many littlesparks, and the effect was very pretty,somewhat as was described before whenthe carbon dust was strewn between theelectrodes. It is more easily and quicklyprepared by giving a sheet of glass a coat-ing of shellac varnish, and then sparinglydusting any powdered conductor over its,surface, using perhaps carbon dust orfilings of metal. By cutting out a stencilfrom a piece of thin card and laying it overthe sparkling plate, the design shows outvery strikingly, and various designs in sten-cils can be prepared, different po
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