d75 RECENT PROGRESS IN PHYSICS. 



interval was enlarged, but never joining the negative glow, there being 

 always a short dark space between. This space, of about one-sixteenth or 

 one-twentieth of an inch was apparently invariable in its extent aind 

 its position relative to the negative rod ; nor did the negative glow vary. 

 Whetlier the negative ends were inductive or inducteous the same effect 

 was produced." 



Similar phenomena were obtained with balls instead of the rounded 

 ends of rods. 



§ 88. Conveciive discliarge. — The dielectric being penetrated by the 

 spark, the brush, and also by the glow, Faraday calls this form of i 

 discharge the disruptive discharge. With the brush, and still more 

 with the glow, another form of discharge appears, making itself mani- 

 fest by the so-called electrical wind. This is owing to the ])article8 of i\ 

 the dielectric, in close contact with the charged conductor, (on the end ' 

 of the electrified rod,) receiving an electrical charge, in consequence of 

 which they are repelled ; and by a repetition of this action the conduc- 

 tor is discharged. 



" Why a point should be so exceedingly favorable to the production 

 of currents is evident. It is at the extremity of the point that the 

 intensity necessary to charge the air is first acquired ; it is from thence 

 that the charged particle recedes ; and the mechanical force which it im- 

 presses on the air to form a current is in every way favored by the shapes 

 and position of the rod whose point forms the termination." — (1573.) 



Particles of dust floating in the air favor the escape of electricity. 



" On using oil of turpentine as the dielectric^ the action and course 

 of small conducting, carrying particles in it, can be well observed." 



" A very striking effect was produced on oil of turpentine, which, 

 whether it was due to the carrying power of the particles in it, or to 

 any other action of them, is, perhaps, as yet doubtful. A portion of 

 that fluid in a glass vessel had a large uninsulated silver dish at the 

 bottom, and an electrified metal rod, with a round termination, dip- 

 ping into it at the top. The insulation was very good. The rod end, 

 with a drop of gum water attached to it, was then electrified in the 

 fluid ; the gum water soon spun off in fine threads, and was quickly 

 dissipated through the oil of turpentine. By the time that four drops 

 had in this manner been commingled with a pint of the dielectric, the 

 latter had lost by far the greatest portion of its insulating power ;" 

 " the fluid was slightly turbid. Upon being filtered through paper 

 only, it resumed its first clearness, and now insulated as well as be- 

 fore."— (1571.) 



"Conducting fluid terminations, instead of rigid points, illustrate in 

 a very beautiful manner the formation of the currents, with their 

 effects and influence in exalting the conditions under which they were 

 commenced. Let the rounded end of a brass rod, 0.3 of an inch, or 

 thereabouts, in diameter, point downwards in free air ; let it be amal- 

 gamated and have a drop of mercury suspended from it, and then let 

 it be powerfully electrized, the mercury will present the [)henomenon 

 of gloio ; a current of air will rush along the rod and set off from the 

 mercury directly downwards, and the form of the metallic drop will be 

 slightly affected, the convexity at a small part near the middle and 

 lower part becoming greater, whilst it diminishes all round at plac-^'-' 

 a little removed from this spot." — (1581.) 



