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XXXIII. On the Gold Fish of Franklin. 



IN a note at the foot of page 250 of the 37th volume of the 

 Philosophical Magazine, a question of interest both in a me- 

 chanical and electrical point of view is suggested by the follow- 

 ing statement of Prof. W. Thomson : — " The phenomenon of a 

 solid body," writes Mr. Thomson, "hovering freely in the air, 

 in stable equilibrium, without any external support, has never, I 

 am convinced, been witnessed as the result of any electrical or 

 magnetical experiment." An experiment described by Franklin, 

 and redescribed by Prof. Srtsczek of Pesth*, without any know- 

 ledge of what Franklin had done previously, seems to furnish the 

 precise fact alluded to by Prof. Thomson. If the knob of a 

 charged Ley den jar be caused to approach a number of scraps of 

 gold-leaf, the consequent jumping of the leaves is well known. 

 If a certain shape be imparted to the gold-leaf, when the knob is 

 approached the leaf is attracted and moves towards the knob ; 

 but, before it reaches the latter, it is arrested, and hovers in the 

 air, like a fish in water. When the atmosphere is dry, the leaf 

 can be preserved swimming for hours together " without any 

 external support or constraint." 



The following description of the experiment by Prof. Srtsczek 

 is taken from Poggendorff s Annalen, vol. lxxxviii. p. 493. 



Let a small Leyden jar which can be held conveniently in the 

 hand be charged with, say positive, electricity. Let the knob be 

 gradually brought near to several bits of gold-leaf lying upon 

 clean paper, from 6 to 12 lines in length, and from a line to a 

 line and a half in width : they may be rectangular, lozenge- 

 shaped, trapezium-shaped or triangular. 



A jumping of the leaves immediately commences, but soon 

 the remarkable fact will be witnessed that one or more of the 

 scraps will suddenly halt in their movement, and remain freely 

 floating in the air ; sometimes rotating round the knob of the 

 jar, and showing a tendency to rotate round their own axes. 



The knob must reach several inches above the insulated rim 

 of the jar, so that scraps which hover at a considerable distance 

 may not be attracted by the rim. At the conductor of a ma- 

 chine the swimming of the gold-leaf is also seen at a much 

 greater distance (a foot for example), but the experiment does 

 not succeed so quickly. The leaves must be smooth, and of an 

 elongated shape. 



With the same strength of charge, portions of gold-leaf, 

 equally long, but of different shapes, hover at different distances 

 from the knob. 



* And, we believe, exhibited in a modified form by Prof. Faraday in bis 

 public lectures. 



Q2 



