

Intelligence and Miscellaneous Articles. 393 



free from powder and stood out very distinctly against the thickly co- 

 vered ground ; in many of them there was in the middle a small heap 

 of dust. The diameter of the circles did not much vary generally ; 

 only towards the edge of the coating did they seem somewhat larger. 



The lower plate exhibited no places free from powder, but only 

 small solid circles, and upon them little stars. 



About the edge of the coatings (that is, upon the corresponding 

 places of the uncoated sides) there was a circle almost free from pow- 

 der, which was enclosed in a ring which gradually thinned off towards 

 the outside. When the action of the apparatus was continued a little 

 longer, nearly all the powder travelled towards this external ring, and 

 the parts of the plate over the coatings were almost free from dust. 



If the two poles be interchanged, the figures become reversed ; that 

 is, the dust-free places are found upon the lower, and the stars upon 

 the upper plate. 



If the distance of the two plates is made somewhat greater, by 

 placing on each other several of the above-mentioned pieces of glass, 

 the diameter of the figures also increases, as is seen from the follow- 

 ing Table, in which d=\'6 millim. : — 



Diameter of the circles. 



Distance of the nlates In the centre At tbe edge 



Distance ot the plates. of the plate of tne plate> 



d 2-1 2-7 



2d 3'8 4-6 



3c? 4-8 6-4 



4d 7-2 7'8 



Here, as the distance increases, the dust-ring moves wider and 

 wider outwards. 



An exchange of the plates for such as are of thinner glass, or a 

 change in the diameter of the coatings, has no influence on the 

 figures ; but it is necessary to alter the duration of action of the ap- 

 paratus to obtain similar figures under circumstances thus altered. 



It may seem surprising that the figures are so similar to Lichten- 

 berg's ; but it is more surprising that on the plate with whose coat- 

 ing the positive pole is connected, and upon which, therefore, from 

 electrical laws, negative electricity must accumulate, the stars ap- 

 pear, while the regular circles are exhibited upon the other plate. 



But this apparent contradiction is removed if, instead of the nu- 

 merous breaks which Ruhmkorff's coil yields, a single one is effected 

 by hand, and thus a single discharge passes through the system. 



This being premised, by correctly regulating the inducing current, 

 only a small number of figures are obtained, but these are very beau- 

 tiful and like Lichtenberg's. For it is observed that both plates, 

 even the upper one, which was not covered with dust, had become 

 coated with a uniform layer of the powder, which was only interrupted 

 by individual figures. 



On the plate whose coating is connected with the positive pole 

 these figures are very regular circles free from powder, whose ex- 

 ternal diameter is pretty well double that of the thickly powdered 

 central spot. 



On the other plate are also circles of the external diameter of the 



