198 J. Trowbridge — Oscillations of Lightning discharges 



summer hotel which was lighted by incandescent lamps, I was 

 much interested to observe that the lamps blinked at every 

 discharge of lightning, although the interval which elapsed 

 between the blinking and the peals of thunder showed that 

 the storm was somewhat remote. This effect was doubtless 

 due to induction produced by the surging of the lightning dis- 

 charges. On the occasion of a heavy discharge the lights were 

 completely extinguished, although no fuse was burned. My 

 observation of this effect of lightning upon electric light cir- 

 cuits also leads me to believe that the system of carrying elec- 

 tric light wires along gas fixtures where both gas fixtures and 

 electric light fixtures are combined is fraught with great 

 danger. If there is a leakage of gas at the joints of the gas 

 pipes or through a sand hole in the casting of the pipes elec- 

 tric sparks arising through resonance effects or from ordinary 

 passage to earth of an electric charge brought into the build- 

 ing by the electric wires can ignite the escaping gas and pro- 

 duce a mysterious conflagration. Such a conflagration was 

 averted in the hotel in which I noticed the blinking of the 

 lamps only by the careful scrutiny of an attendant who no- 

 ticed a jet of gas from a pin hole in the gas fixtures imping- 

 ing on the wood work. During the storm a minute electric 

 spark had ignited the escaping gas. Electric light wires and 

 gas pipes should never be contiguous ; for no lightning guard 

 or protector can ensure that minute sparks, due in some cases 

 to resonance effects, may not arise. 



The study of the disruptive or oscillatory discharge of light- 

 ning is closely connected with that of the brush discharge and 

 that of the phenomenon of the Aurora Borealis ; for the disrup- 

 tive discharge if it is an oscillatory discharge ceases to be disrup- 

 tive after a few hundred thousandths of a second, as figures 1 

 and 2 show, and partakes of the nature of a brush discharge. 

 The zigzag fissures in the air disappear and only the spark 

 terminals glow. Recent experimenters have exhibited, as a 

 marvel, the lighting of a vacuum tube through the human 

 body by grasping one terminal of a suitable transformer with 

 one hand and by holding the vacuum tube in the other hand. 

 It must be remembered, however, that the lines of force pro- 

 ceed from the hand which holds the vacuum tube through the 

 air and the walls or floor of the room to the other terminal of 

 the transformer. We can change this brush discharge or 

 luminosity at either terminal of a transformer into a disrup- 

 tive discharge by lessening the distance between the terminals 

 or by increasing the electromotive force. 



I am fully aware that the oscillatory discharge of lightning 

 with its disruptive effects 1 have noted — its permanence of 

 path and the fading of the disruptive discharge into the brush 



