28 Recent Advances in Electricity. 



circuit for the currents which produce the visible luminosity. 

 It would seem that the human organism is not able to vibrate 

 fast enough to respond to such an excitation. This is in accor- 

 dance with other well-known facts in connection with nervous 

 stimulus. The bobbing of a gas flame is very annoying when 

 it is slow, and increasingly painful when it is a little faster ; but 

 when it is as fast as ico bobs per second it is not perceived at 

 all. Another noteworthy result is the ability to dispense with 

 conducting communication. It is not necessary to have wires 

 passing through the ends of a vacuum tube, or if such wires are 

 present it is not necessary to connect them with the terminals 

 of the source of electricity. The inlEluence which produces 

 luminosity in the tube is able to make its way through the 

 glass. A large cubic space of air can be filled with the influence 

 by hanging up a large sheet of metal on insulating supports and 

 connecting it with one terminal of the source, while a similar 

 plate connected with the other terminal hangs at the other side 

 of the space. Any vacuum tube held in the intervening space 

 ivill become luminous. It appears from these experiments that 

 air, or at all events rarefied air, is very easily thrown into such 

 a state of vibration as to become luminous, by an exciting cause 

 which operates by an extremely rapid succession of impulses — 

 that, in fact, very little energy is required to produce light if 

 we can only find the means of applying our energy in the right 

 way. Other facts may be quoted confirming the same view. 

 Every one must have seen the phosphorescence of fish lying 

 on a shelf in a dark pantry, and many of us have seen beautiful 

 displays of phosphorescence on the surface of the sea — due, I 

 believe, to a small animal called the nociiluca. I have 

 scooped up phosphorescent water from Kingstown harbour, 

 and seen the little bright objects with which it abounded. 

 The glowworm is well known by name, though many people 

 have never seen it. I have seen it once or twice in England 

 and taken it in my hand, its light continuing all the time to be 

 emitted. It was a wingless beecle, about an inch long. Much 

 more vivid is the light of the firefly, which I have seen on 



