550 Progress in Science. [Oaober, 



shifted to, the point where the bar would most influence the coil. The advan- 

 tages gained in economy of construction (by the use of smaller magnets) and 

 in compactness of arrangement are the chief points in the improvement. With 

 the Gramme machine a striking experiment, first made by MM. Gaston- 

 Plante and A. N. Breguet, has been recorded by them in " Les Mondes.'' 

 They charge a Plante secondary couple (coiled sheets of lead in dilute 

 sulphuric acid), and, in place of discharging the couple, they allow it to 

 remain in communication with the machine ; when, if the machine be suddenly 

 and completely stopped by the hand, the coil, on the removal of the hand's 

 resistance, will re-continue to revolve, not in an opposite direction, but in the 

 same direction as when charging the secondary couple, for a period of two or 

 three minutes. Nothing would appear more paradoxical than that the machine 

 should continue to turn in the same direction. But the explanation is simple, 

 and is given by the experimenters in the following words: — " If we consider 

 the direction of the current furnished by the machine that of the current given 

 back by the secondary couple, which is inverse to the preceding, and if we 

 take into account the action which results, we shall find that, according to the 

 laws of induction and electro-dynamics, the movement of rotation should be in 

 the direction indicated by experiment. And if we observe that the secondary 

 couple has an intensity temporarily superior to that furnished in a given time 

 by the machine, we shall easily be able to perceive that the discharge from the 

 secondary couple overcomes that of the machine." 



The next step in electrical science most probably will be in improved 

 application of the electric light. Recently, at St. Petersburg, experiments 

 have been made by Messrs. S. A. Kosloff and Co. with the invention of 

 M. Ladiguin. This invention consists in the use of one piece of charcoal or 

 other bad conductor, which, being attached to a wire connected with a magneto- 

 electric machine, is placed in a glass tube from which the air is exhausted, and 

 replaced by a gas which will not at a high temperature combine chemically 

 with the charcoal. This tube is then hermetically sealed, and the machine 

 being set in motion, the charcoal becomes gradually and evenly heated, and 

 emits a soft, steady, and continuous light. Taking into consideration the fact 

 that one machine worked by a small three-horse power engine is capable of 

 lighting many hundred lanterns, it is evident that a great step has been gained 

 to the end of lighting our streets by means of electricity. 



Practically, perhaps, the greatest good has been achieved by the application 

 of the duplex system of working on our telegraphic lines and cables. By this 

 system the capacity of our lines for work are doubled, and consequently the 

 capital invested should repay doubly what it would on the single transmission 

 system. The improvements in this country come chiefly from Mr. W. H. 

 Preece, C.E., of the Post Office telegraphs. The Americans have long em- 

 ployed a system similar in effect, invented by Mr. J. B. Stearns. The system 

 apparently most in favour is that founded on the use of the Wheatstone 

 bridge ; and, indeed, the system may be described briefly as the arrangement 

 at each station of such a bridge system as will have its galvanometer needle 

 deflected by a current other than that of its own battery. This is effected by 

 substituting the instrument of the sending station for the galvanometer of the 

 bridge, putting equal or proportional resistances into two branches, the line 

 wire into the third branch, and a resistance compensating that of the 

 line wire into the fourth. An out-going current thus possesses opposite 

 and equal potentials at the terminals of the instrument, but an in-coming 

 current finds only a divided circuit, in one branch of which is the instrument. 



Amongst the electrical apparatus meeting the wants of the laboratory and 

 lecture-table especially, may be classed the new ozone-generator invented by 

 Mr. Tisley. The construction of this instrument may be described as follows : — 

 On each end of a piece of glass tube of uniform bore is placed a brass cap, 

 bored with two holes, and coated internally with shellac. In the interior of 

 this glass tube, and of a diameter scarcely less than that of the tube itself, but 

 not quite so long, is placed a thin hollow brass box, with its surface made as 

 true as possible by turning in a lathe. This brass box is placed concentrically 



