96 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
difficulty, even with the revolving mirror of the microscope, which must be caused to 
revolve at different velocities to render them apparent ; with a moderate magnifier, a 
hand lens, the barrel-shaped surrounding appears as if shaded with lines across it. 
As one examines the arc with the mirror revolving at a great velocity, evidence of the 
carrying of minute particles is given by streaks of bright light, which cross the field. 
The arc in hydrogen, with the point positive, is shown in 2, fig. 23 ; the central 
spindle is surrounded by a beautiful blue halo, like a glass shade illumined by 
Fig. 22. 
Fig. 23. 
fluorescent fight, and very brilliant on the disc ; with 8040 cells the spark jumped on 
one occasion 0*562 inch when the point was positive, and only 0*462 inch when 
negative; the ratio of negative to positive 1 = 0*822. With 4 megohms’ resistance in 
the circuit, the streaming discharge from the point positive, at 0*502 inch distance, 
was carmine in colour. This distinctive colour is a proof that the gas in which the 
discharge takes place is the carrier of electrification in the streamer discharge. The 
appearance of the arc when the point is negative is shown in 4 ; it moves about very 
