1892.] on Alternate Currents of High Potential and Frequency. 641 



or multiple gap througli tlie primary of tlie second coiL To insure 

 the action of tlie gap, the arc was blown out by a magnet or air- 

 blast. To adjust the potential in the secondary a small oil con- 

 denser was used, or polished brass spheres of different sizes were 

 screwed on the terminals and their distance adjusted. 



When the conditions were carefully determined to suit each 

 experiment, magnificent effects were obtained. 



Two wires, stretched through the room, each being connected to 

 one of the terminals of the coil, emit streams so powerful that the 

 light from them allows distinguishing the objects in the room ; 

 the wires become luminous even if covered with thick and most 

 excellent insulation. When two straight wires, or two concentric 

 circles of v^ire, are connected to the terminals, and set at the proper 

 distance, a uniform luminous sheet is produced between them. It 

 was possible in this way to cover an area of more than one meter 

 square completely with the streams. By attaching to one terminal 

 a large circle of wire and to the other terminal a small sphere, the 

 streams are focussed upon the sphere, produce a strongly lighted 

 spot upon the same, and present the appearance of a luminous cone. 

 A very .thin wire glued upon a plate of hard rubber of great thick- 

 ness, on the opposite side of which is fastened a tinfoil coating, is 

 rendered intensely luminous when the coating is connected to the 

 other terminal of the coil. Such an experiment can be performed 

 also with low frequency currents, but much less satisfactorily. 



When the terminals of such a coil, even of a very small one, 

 are separated by a rubber or glass plate, the discharge spreads over 

 the plate in the form of streams, threads, or brilliant sparks, and 

 affords a magnificent display, which cannot be equalled by the largest 

 coil operated in the usual ways. By a simple adjustment it is 

 possible to produce with the coil a succession of brilliant sparks, 

 exactly like with a Holtz machine. 



Under certain conditions, when the frequency of the oscillation 

 is very great, white phantom-like streams are seen to break forth 

 from the terminals of the coil. The chief interesting feature about 

 them is, that they stream freely against the outstretched hand or 

 other conducting object without producing any sensation, and the 

 hand may be approached very near to the terminal without a spark 

 being induced to jump. This is due presumably to the fact that a 

 considerable portion of the energy is carried away or dissipated in 

 the streamers, and the difference of potential between the terminal 

 and the hand is diminished. 



It is found in such experiments, that the frequency of the vibra- 

 tion and the quickness of succession of the sparks between the knobs 

 affect to a marked degree the appearance of the streams. When 

 the frequency is very low, the air gives way in more or less the 

 same manner as by a steady difference of potential, and the streams 

 consist of distinct threads, generally mingled with thin sparks, 

 which probably correspond to the successive discharges occurring 



