Intelligence and Miscellaneous Articles. 467 



A SPARK-ADJUSTER FOR THE HOLTZ MACHINE. 

 BY JAMES J. MINOT. 



In the Annalen der Physik unci Chemie, Bd. cxxxvii. p. 452, and 

 Bd. cxxxix. p. 509, under the title of " Schwache elektrische Funken 

 in Luft, von P. Riess," a method is described of obtaining different 

 kinds of electric sparks from the Holtz machine. 



The following method seems to be preferable to that described in 

 the above-mentioned articles: — Having insulated the outer coating 

 of the two Leyden jars which form a part of the ordinary Holtz 

 machine, short thick wires were connected with these outside 

 coatings and terminated in two brass pointers or conductors, so 

 arranged that the distance between them could be varied at pleasure. 

 At first the conductors were placed in connexion with each other ; 

 it was then found that a series of sparks were given off between 

 the conductors of the machine. The extreme length of spark ob- 

 tainable with the machine which was used was 20 centims. The 

 sparks so obtained were large and luminous, passing only at inter- 

 vals, and requiring a certain electric tension before they would 

 leap across the space. Then the pointers connected with the outer 

 coatings of the Leyden jars were drawn apart about 13 millims. ; 

 it was then found that a succession of fine thread-like sparks 

 passed across the space separating the conductors of the machine, 

 whereas there was no such appearance between the pointers con- 

 nected with the jars. But at intervals a larger spark, not so bright 

 as the normal spark of the machine, would jump across the con- 

 ductors ; and simultaneously with this a similar spark passed 

 between the pointers. This fine line of sparks was found to have 

 a peculiar form, being brightest and largest at the ends of the con- 

 ductors of the machine, fading away to a lighter and redder tint, 

 and being of a thread-like character in the space between the knobs 

 of the conductors. 



It was found, if the distance between the conductors of the 

 machine exceeded a little that between the pointers connected with 

 the Leyden jars, that no large sparks passed between either set of 

 conductors, but only a series of thread-like discharges. When the 

 distance between the conductors of the machine was less than that 

 between the pointers, a similar result was obtained. When the 

 pointers were but a few millimetres apart, a continuous loop-like 

 discharge passed between them, which was not interrupted by the 

 occasional passage of a bright spark, and was not coincident in path 

 with the latter. By varying the distance of the pointers of the 

 Leyden jars, the number and character of the sparks could be 

 changed at will. This method possesses the advantage that by an 

 easy adjustment of these pointers the form of the electric spark can 

 be readily studied. In experimenting upon the passage of the 

 spark through different media, we can by this method diminish the 

 diameter, so to speak, of the spark, and can change quickly from 

 the spark discharge to that of the brush. The change in tone of 

 the sound of the discharge, when the distance between the pointers 

 is varied, is quite marked. — Silliman's American Journal, May 1874. 



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