272 



ELECTEICITY. 



being through tho earth ; and it is quite clear 

 that they would be so received and read at 

 fifty stations in the neighborhood all at once. 

 The explanation is obvious enough : the poten- 

 tial of the ground in the neighborhood of the 

 stations is alternately raised and lowered by 

 the powerful battery used to send the American 

 signals. The potential of the sea at the other 

 end of the short insulated line remains almost 

 if not wholly unaffected by these, and thus the 

 island acts like a sort of great Leyden jar, con- 

 tinually charged by the American battery, and 

 discharged in part through the short insulated 

 French line. Each time the American operator 

 depresses his sending-key, he not only sends a 

 current through his lines, but electrifies the 

 whole island, and this electrification is detected 

 and recorded by the rival company's instru- 

 ments. 



The Electric Light in War. The Paris cor- 

 respondent of tho Engineer writes that the 

 French made great use of the electric light in 

 the defence of that city. One of the varieties 

 of apparatus set up on Montmartro by M. 

 Bazin was electro-magnetic. The central 

 cylinder supported four series of double coils, 

 covered with copper wire enveloped in silk. 

 The cylinder was rotated by a steam engine 

 of three horse-power, making about 400 revo- 

 lutions a minute. The lamp used was of the 

 ordinary form, with the Foucault and Duboscq 

 regulator. The reflector was parabolic, and 

 the whole surrounded by a shield, to hide it 

 from the Germans. The light, from its elevated 

 position, commanded the whole of Paris and 

 the surrounding plains. A spectator on Mont- 

 martre could see distinctly the details of the 

 facade of a building 2,600 metres off; at 2,900 

 metres a man could be seen standing at a win- 

 dow ; at 3,000 metres a mass of cavalry or in- 

 fantry was distinguishable ; and at 4,000 metres 

 the dome of the Invalides, with its bands of 

 gold, looked brilliant. On the ramparts, 800 

 metres from Montmartre, the light was suffi- 

 cient to read a newspaper by. Thus, though 

 the practical effect of tho lamp only extended 

 about 300 metres from its position, the field 

 was illuminated to the extent of 700 metres 

 for the benefit of all placed between the light 

 and its object. A sentinel on the ramparts 

 could see about 3,000 metres from the enceinte, 

 and, by this means, strict watch was kept 

 upon the plains around the city at night, as 

 far, in one direction, as 1,000 metres beyond 

 St. Denis. On one of the French corvettes 

 the same apparatus was adapted for a night- 

 telegraph, with the addition of a system of 

 flashes and the aid of a colored lens, and sig- 

 nals made distinctly visible at a distance of 

 eight miles. 



Electro-Heating. "W. Leigh Burton, of 

 Eichmond, Va., describes, in Van Nostrand's 

 Engineering Magazine, a new invention for 

 utilizing electricity for heating purposes. He 

 takes a magneto-electric machine, like "Wilde's, 

 and connects with it a chain or coil made up 



of alternate obstructions and free conductors. 

 The obstructions are pieces of platinum wire, 

 say one-hundredth of an inch thick, and the 

 free conductors or radiators are pieces of 

 copper about one-eighth of an inch thick. 

 These radiators also perform the part of reser- 

 voirs so as to produce an equal distribution 

 of the current, and hence, when a sufficiently 

 powerful current is sent through any length 

 of chain, the same caloric effects take place in 

 every portion of it. His invention he thinks 

 peculiarly adapted to railway-cars. The mag- 

 neto-electric engine would be placed under 

 the car, and operated from an axle of the car- 

 wheels ; and by the chains heat would be con- 

 ducted to metallic plates put under each seat, 

 or not so thickly, and sufficient heat radiated 

 from those points to warm the cars. The au- 

 thor, in this connection, gives an account of 

 another invention which he terms a " circuit- 

 changer," by the use of which large magneto- 

 electric machines could be dispensed with, 

 smaller ones being able to do the same heat- 

 ing work. He says : 



By means of another invention of the writer's, 

 which he has termed a " circuit-changer," very large 

 machines may be dispensed with entirely ; and of 

 course the smaller the machine the less it would cost 

 and the less power it would require to operate it. 

 This instrument consists of a revolving shaft or bar- 

 rel, one end of which is kept in constant connection 

 with the battery or machine, by means of a brake. 

 Placed on the shaft are a number of points arranged 

 spirally, so that in revolving the instrument no two 

 points approach the same line at the same time. 

 Corresponding to these points are springs, and when 

 the apparatus is in operation each point is brought 

 consecutively in contact with, corresponding springs. 

 To give a better idea of the contrivance, it might be 

 compared to a musical box, the difference being that 

 in revolving it a contact is made instead of a musical 

 sound. By means of this instrument a current of 

 electricity may be sent consecutively through as 

 many different circuits as there are points on the 

 cylinder, the only limit being the number of the lat- 

 ter that can be placed on a cylinder of a certain 

 length and diameter. It is easy to understand, there- 

 fore, if a current of electricity of a certain power will 

 produce certain calorific effects by being sent through 

 a certain circuit at the rate of, say five hundred times 

 in a minute, it would produce the same effects by 

 being sent through any other, or one hundred more, 

 for the reason that the same current is sent through 

 each different circuit the same number of times per 

 minute ; and, but for the wear which it would neces- 

 sarily entail on the instrument, it could be revolved 

 with such rapidity as to make it in each very nearly 

 continuous. 



In order to warm a railway-car, then, it would re- 

 quire a circuit-changer with points on it correspond- 

 ing to the number ot seats ; and, if a passenger should 

 find the heat under his feet uncomfortable, he could 

 easily, by a contrivance for the purpose, cut off the 

 current, and at once cause an abatement of it. 



Chronoscope. Such is the name given to an 

 invention of Captain Noble, of England, for 

 ascertaining the movement of a projectile 

 within a gun thus supplementing the office of 

 a chronograph, which records the speed of a 

 ball after it leaves the piece. The machine 

 comprises wheel-work set in motion by a heavy 

 weight, a dial which indicates the rate of 

 motion, and a series of disks rotating on an 



