DISRUPTIVE DISCHARGE — BRUSH-INTERMITTING. Ill 



1428. The single brushes could easily be separated to eight or ten times their 

 own width, but were not at the same time extended, i. e. they did not become more 

 indefinite in shape, but, on the contrary, less so, each being more distinct in form, 

 ramification, and character, because of its separation from the others, in its efl^ects 

 upon the eye. Each, therefore, was instantaneous in its existence (1436.). Each had 

 the conical root complete (1426.). 



1429. On using a smaller ball, the general brush was smaller, and the sound, 

 though weaker, more continuous. On resolving the brush into its elementary parts, 

 as before, these were found to occur at much shorter intervals than in the former 

 case, but still the discharge was intermitting. 



1430. Employing a wire with a round end, the brush was still smaller, but, as be- 

 fore, separable into successive discharges. The sound, though feebler, was higher 

 in pitch, being a distinct musical note. 



1431. The sound is, in fact, due to the recurrence of the noise of each separate 

 discharge, and these, happening at intervals nearly equal under ordinary circum- 

 stances, cause a definite note to be heard, which, rising in pitch with the increased 

 rapidity and regularity of the intermitting discharges, gives a ready and accurate 

 measure of the intervals, and so may be used in any case when the discharge is heard, 

 even though the appearances may not be seen, to determine the element of time. So 

 also, when, by bringing the hand towards a projecting rod or ball, the pitch of the 

 tone produced by a brushy discharge increases, the effect informs us that we have 

 increased the induction (1374.), and by that means increased the rapidity of the 

 alternations of charge and discharge. 



1432. By using wires with finer terminations, smaller brushes were obtained, until 

 they could hardly be distinguished as brushes ; but as long as sound was heard, the 

 discharge could be ascertained by the eye to be intermitting ; and when the sound 

 ceased, the light became continuous as a glow (1359. 1405.). 



1433. To those not accustomed to use the eye in the manner I have described, or, 

 in cases where the recurrence is too quick for any unassisted eye, the beautiful 

 revolving mirror of Professor Wheatstone* will be useful for such developments 

 of condition as those mentioned above. Another excellent process is to produce 

 the brush or other luminous phenomenon on the end of a rod held in the hand oppo- 

 site to a charged positive or negative conductor, and then move the rod rapidly from 

 side to side whilst the eye remains still. The successive discharges occur of course 

 in different places, and the state of things before, at, and after a single coruscation 

 or brush can be exceedingly well separated. 



1434. The brush is in reality a discharge between a bad or a non-conductor and 

 either a conductor or another non-conductor. Under common circumstances, the 

 brush is a discharge between a conductor and air, and I conceive it to take place in 

 something like the following manner. When the end of an electrified rod projects into 



* Philosophical Transactions, 1834, pp. 584, 585. 



