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VII. Researches on the Electrical Discharge. 

 By Professor von Bezold*. 



IN the course of the further investigation on the connexion 

 I have recently describedf as existing between the mode 

 of discharge and the character of the dust-figures thereby pro- 

 duced, I strongly felt the necessity of producing the phenomena 

 in question by a more simple apparatus than Ruhmkorff's. 



The first experiments with charged Leyden jars, as well as 

 with the ordinary electrical machine without condensing-arrange- 

 ments, soon showed that with these means only simple figures 

 (that is to say, discharges) could be obtained. 



The observation of the spark is sufficient to prove that the 

 discharge which, with a good conducting circuit only inter- 

 rupted by a break, is alternating, is changed into a simple 

 one by inserting a test-plate J ; for while in the first case the 

 spark is brilliantly luminous, it appears in the second only as a 

 narrow purple line with a bright point towards the positive 

 electrode. 



In order, therefore, to obtain alternating discharges even when 

 the test-plate was interposed, no way was left but the use of a 

 suitable branch or return conductor. 



If this conductor (which goes to earth) is continuous (that 

 is, nowhere interrupted by a break), it is to be expected that the 

 discharge of the conductor through which the electricity is led 

 to the plate will ensue directly after the charge, — that is, that 

 in this conductor one or more alternations of electricity will 

 take place. 



In experiments made with such return conductors, various 

 entirely new and surprising facts were observed which seem 

 suited to serve as starting-points for new inquiries. 



But, before I begin the description of these new facts, I must 

 first mention a simple experiment, which indeed teaches nothing 

 essentially new, but yet contributes materially to the under- 

 standing of the following. 



If the otherwise insulated coating of the test-plate is placed 

 in conducting communication with the source of electricity, while 

 the needle which at other times serves as conductor is connected 

 with the earth, a positive discharge upon the glass surface pro- 

 duces a negative figure, and conversely. 



If the coating be perfectly insulated, while two conductors (A 



* Communicated by the Author, having been read before the Bavarian 

 Royal Academy of Sciences, February 5, 1870. 



t Phil. Mag. S.4. vol. xxxix. p. 392. 



X By test-plate (Probeplatte) I shall in the sequel mean the plate, 

 coated on one side, on which the figures are formed. 



