492 Prof. W. A. Douglas Budge on the 



nature of the charge acquired by the plate, and also the charge 

 upon the air could be indicated (PL VI. fig. 3). 



A box measuring 40 X 30 x 30 cm. having a well fitting door 

 was taken. Through the top a thick plug o£ ebonite was 

 passed, and through this plug a wire was joined to a plate 

 of wire gauze. To the door of the box an insulated plate 

 was attached, so that on opening the door a connexion could 

 be established between the plate and an electroscope, and 

 any charge it possessed indicated. A hole at the bottom 

 allowed of a blast of air being introduced, and another at the 

 top allowed the air and dust to escape (PI. VI. fig. 3). 



Some flour was placed on the bottom of the box and both 

 electrodes earthed. A blast of air was sent in from the 

 bellows, aud after a short time the earth connexion was 

 broken, and the top of the box tapped so as to shake off as 

 much flour as possible from the upper electrode. On putting 

 the electroscope in communication with this electrode, a 

 positive charge was seen to be present. On opening the 

 box and testing the lower plate upon which some of the flour 

 particles had settled, a negative charge was shown to be 

 present. The charges were not as strong as those obtained 

 in the open air, but they were quite sufficiently strong to 

 admit of identification. On repeating the experiment with 

 sulphur, the upper electrode became positive, and the lower 

 one negative. The charge upon the upper electrode was 

 always more marked than that on the lower one, and the 

 small effect in the latter case appeared to be due to (1) the 

 particles of dust giving up their charge to the walls of the 

 box, and (2) the comparative fewness of the particles 

 reaching the plate. 



" Lichtenberg " figures may very readily be obtained from 

 the dust clouds formed in the box used for the last experi- 

 ment ; and a very marked difference is seen when the charges 

 upon the plate are different. 



A cleaned ebonite plate was touched for an instant with 

 the knob of a charged leyden-jar. A cloud of dust was 

 raised in the box, and as quickly as possible the charged 

 plate was put inside. The particles of dust were attracted 

 to the charged surface, and a well-defined " Lichtenberg V 

 figure obtained. If flour was used, the figure was strongly 

 developed when a positive charge had been "splashed" upon 

 the plate; and if sulphur, then the same thing was seen if 

 the charge was negative. Figures, however, could be ob- 

 tained with both charges, but were of a different character. 

 No doubt the electrified air moving with the dust would 

 effect some slight modification. The photographs show some 



