302 Intelligence and Miscellaneous Articles. 



magneto-electrical machine acted more slowly. In like manner; 

 when the brush-discharge was produced from sixteen points in the 

 chimney-pipe of a stove towards the sides, the smoke was almost 

 completely deposited, especially if the points were connected with 

 the negative, and the pipe with the positive electrode of the ma- 

 chine ; and two double induction-machines connected together were 

 used. 



Kundt's dust-circles were also obtained, when the points and 

 the plate were connected with the poles of an induction-machine, 

 and the discharge continued for some time. They are equal for 

 the two electricities. If the metal disk is not dusted with sulphur 

 or lycopodium until the discharge takes place, dust-rings are formed 

 instead of dust-circles. Here also the rings are equal, whether the 

 point is positive or negative. If the point is very close, dust- 

 circles appear surrounded by an annular surface almost entirely 

 free from dust, and again surrounded by slight dust near the edge 

 of the plate. 



With a positive plate 215 millim. in diameter, with a fine nega- 

 tive point at a distance s, the magnitude of the rings is as follows 

 (D a and D* being the outer and inner diameter of the dust-circle or 

 dust-rings, D that of the dusted surface : — 



s 5 10 15 20 30 45 60 millim. 



V a 30 55 75 90 110 135 160 „ 



D,. 35 40 55 65 75 „ 



D 70 100 130 160 >215 mm. 



The explanation of the various figures is ascribed by the authors 

 to the electrification of the badly-conducting particles of dust 

 which lie on the plate, and which in consequence adhere to the 

 plate as in Kundt's figures . If to this is added the electrical aura, 

 it blows the particles away from the middle and lodges them 

 towards the edge, where they adhere in consequence of permanent 

 electrification. 



If, instead of metal plates, vertical networks of 1 centim. width 

 of mesh are used, a horizontal point being brought to within a dis- 

 tance of 7 centim., while the net and the point are connected with 

 the conductors of two influence-machines connected with each 

 other, and if sulphur-powder is dusted on the net while the brush- 

 discharge takes place from a negative poiut, a dust-ring is formed of 

 38 centim. external and 15 centim. internal diameter. If the powder 

 blown through the net is caught on a horizontal paper, a tongue 

 about 15 centim. in width appears free from dust, to which fol- 

 low zones on each side of tolerably dense powder. With a positive 

 point the same result is obtained, except that the dust-free zone is 

 not so distinct. Lycopodium flies further away. 



If a fine point, and a wire gauze of I centim. width of mesh, is 

 placed at a distance s parallel in the electrodes of an induction- 

 machine, and these latter are adjusted at a distance D so that 

 sparks alternately pass between the electrodes, and brush-discharges 

 take place from the point, the following values were obtained for 



