1871.] Electricity. 279 



a certain amount against a given pressure as would be required if the turpen- 

 tine were replaced by air. This will be a little inaccurate, as the coefficient of 

 expansion of a vapour is always greater than that of a permanent gas. Now, 

 this heat thrown in has these effects : a portion, H r , is used simply to heat the 

 gas to raise its temperature ; a second part, H 2 , does internal molecular work, 

 by separating the particles against their own cohesion ; whilst a third, H 3 , 

 expands the gas against the external pressure, and produces the work which we 

 measure in foot-pounds. It is easy to see that Mr. Highton compares these 

 foot-pounds with the whole heat thrown into the gas, H1 + H2 + H3, instead of 

 the heat, H 3 , used in producing'them. In a gas, H 2 is very small, as the expe- 

 riments of Joule and Thomson show ; but in a vapour it is considerable. 

 Mr. Highton's answer to the supposed objector is altogether irrelevant. The 

 objector might have added that the heat also raises the temperature of the gas, 

 and he does not assume that this is equivalent to work measured by foot- 

 pounds, though it is only that some of the heat is used to effect the expansion 

 and the heating, whereas Mr. Highton unwittingly assumes that none of the 

 heat is so applied, but that all goes to lift the weight. 



ELECTRICITY. 



The Passage of Electrical Currents through Rarefied and other Atmospheres. 

 — Mr. C. F. Varley, the electrician, has recently made several new discoveries 

 in relation to the passage of electricity through rarefied gases, and through the 

 atmosphere at its normal pressure. Some of these discoveries were made 

 known in papers read before the Royal Society a few weeks ago, and several 

 were shown at General Sabine's soiree at Burlington House a fortnight since. 

 In his experiments he uses Geissler's vacuum tubes, which have been ex- 

 hausted by chemical means to a degree ten or fifteen times as attenuated as 

 the vacuum which can be produced by the best made air-pump. Such a 

 tube shows stratifications in the light when an electrical current is passed 

 through it. He has discovered that four distinct kinds of luminous dis- 

 charge may be produced by graduating the strength of the current flowing 

 through the tube, b)^ introducing various amounts of resistance into the circuit. 

 The results may be summed up as follows : — 1. With an extremely feeble 

 current of high intensity and small quantity, the luminous positive pole is alone 

 visible. This light, although scarcely visible to the eye in the darkest room, 

 photographs itself perfectly on a photographic film of wet sensitised collodion ; 

 an exposure of thirty minutes with a double-combination portrait lens is, how- 

 ever, necessary. 2. On diminishing the resistance so as to increase the quan- 

 tity, a tongue of light projects from the positive towards the negative pole, and 

 the two poles become luminous. 3. On still further augmenting the quantity, 

 the negative pole only becomes luminous. 4. Lastly, on passing a momentary 

 current of great quantity and intensity through the tube, the positive pole alone 

 is luminous, but in spots only, and not all over as in the first case. All these 

 experiments have been photographed by Mr. Varley. 



A bell struck in a vacuum produces no noise. In the performance of the 

 fourth of the foregoing experiments, the momentary discharge of electricity 

 through the vacuum produces a sharp distinct " click " of a peculiar sound. 



Mr. Varley has also discovered that four different kinds of discharge may be 

 obtained through air, between the two conductors of a powerful Holtz's 

 electrical machine, capable of giving sparks from eight to eleven inches in 

 length. In the course of his experiments, he observed one kind of discharge, 

 which seems to clear up the mystery hanging over that very rare phenomenon 

 — ball lightning. 



When a small strip of paper, pointed at both ends, is attached to the knob of 

 the negative conductor of" the Holtz's machine, the two ends of the paper being 

 bent, so as to point towards the knob of the positive conductor, and when the 

 two conductors, fully and continuously charged, are placed rather too far apart for 

 the spark to pass, two bright spots are seen upon the negative conductor. The 

 first impression with regard to these spots is that there are two particles of 

 dust on the positive pole, acting as points to throw off electricity. That such 

 is not the case is easily shown by rotating, first the negative, and then the 



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