ELECTRICITY. 



411 



such a light, by timing successive flashes ac- 

 cording to a prearranged order of long or short 

 flashes and repetitions, thus becomes practica- 

 ble. Such a system of flashing lights with the 

 Fresnel lenses is already to some extent in use ; 

 and for field operations, as well as in some 

 cases for lighthouses, it may be rendered of 

 great value. For a system of this sort, the 

 name of Photo-Telegraphy has been proposed. 

 Another mode of this telegraphing by light, is 

 that of successive flashes of different colors. 

 Mr. Wm. C. Bridges, of Philadelphia, has in- 

 vented an apparatus for this form of light sig- 

 nals, consisting of a tube and lens, with adjust- 

 able mirrors as may be required, and different- 

 ly colored and also opaque glass slides, to be 

 moved at will in front of the lens. The electric 

 or other light shining continually into the tube, 

 the slides determine by color and intervals of 

 the flashes the character of the signals made. 

 In any mode, the light signals could be, by a 

 customary system, or by systems, secret to all 

 but initiated parties. 



Application of the Electric Light to Mining 

 Purposes. MM. Dumas and Benoit have de- 

 vised a compact and highly portable appa- 

 ratus, its entire bulk not exceeding that of a 

 small carpet bag, including a battery, a Ruhm- 

 korff coil, and a Geissler's tube, within which 

 the light is generated; the arrangement pro- 

 ducing sufficient illumination to enable a 

 miner to work by it, as by a Davy's safety- 

 lamp. This light serves equally well in an at- 

 mosphere in which all others fail ; while, the 

 light being cold, and its production wholly 

 within a confined tube into which gases have 

 no access, it is perfectly safe against explosion 

 under all circumstances. The arrangement will 

 give light for 12 consecutive hours with no at- 

 tention save that the workman must occasion- 

 ally agitate the carbons by means of a rod ; and 

 it is instantaneously lighted or extinguished at 

 will, while no injurious emanation arises from 

 it. From results obtained with the use of 

 Becquerel's fluorescence-tubes, it is supposed 

 that the luminous effects are susceptible of 

 further great improvement, both in respect to 

 duration and intensity. 



This light, or some other similar in principle, 

 is certain to possess value for other purposes 

 besides mining. Thus, in coal oil factories the 

 best safety lamps are said to fail, since the sub- 

 tile benzole vapors may take fire through the 

 finest wire gauze. Here, the electric lipht. with- 

 in a closed tube, would be entirely safe ; and it 

 would also prove peculiarly appropriate where 

 danger from the dashing of water may exist, as 

 in the interior of gunboats and steam rams, and 

 even in diving bells. 



Engraving by Electricity. The cylinders of 

 copper brass employed in the printing of wo- 

 ven fabrics and paper-hangings are by a recent 

 invention engraved by means of electricity 

 the voltaic current being so applied as to com- 

 municate the necessary movements to certain 

 portions of the apparatus. The cylinders to be 



engraved are first coated on their outer surface 

 with a thin film of varnish, of such nature as 

 to be capable of resisting the continuous action 

 of the strongest acids. The requisite number 

 of copies of the original design are then traced 

 or scratched simultaneously by a series of 

 diamond points, which are arranged on the 

 machine parallel with the axes of several cylin- 

 ders operated on at the same time. Each 

 diamond point is in correspondence with a 

 small temporary magnet ; and the original de- 

 sign having been previously etched on a metal 

 cylinder fitted in with a non-conducting sub- 

 stance, and this cylinder being made to revolve 

 in contact with a tracing point, it results that 

 the current passes, or is interrupted, through 

 the entire series of coils of the electro-magnets, 

 securing the contact of each diamond point 

 with its corresponding cylinder, or the reverse, 

 according as the point rubbing on the first cyl- 

 inder touches a conducting or anon-conduct- 

 ing portion of its surface : in this way, while 

 the cylinders all revolve at the same rate, the 

 diamond points are made to cut upon all but 

 the first, or are raised from them, and at the 

 same moments. The metallic surface is hence 

 exposed in like parts on all the cylinders oper- 

 ated on ; and a bath of nitric or other acid be- 

 ing afterward used to etch or deepen the en- 

 graved portion, the operation is completed. By 

 interposing suitable connections, the engrav- 

 ings can be enlarged or diminished to any ne- 

 cessary extent from the same original. 



Electric Despatch. The experiment in which 

 a bobbin or coil of wire conducting a current 

 of electricity draws within itself an iron rod of 

 the length of such bobbin, or even sustains the 

 rod, when the arrangement is vertical and the 

 power of the current sufficient, against the 

 force of gravity, is now familiarly known. 

 Availing himself of the converse of this prin- 

 ciple, Mr. Henry Cook, of Manchester. England, 

 has constructed and patented an electric pro- 

 peller for transporting despatches, letters, and 

 other small articles. A line of miniature rail- 

 way is laid within a tube or pipe extending 

 between the points of communication, and 

 formed of a series of hollow electric coils or 

 electro-magnets. The carriage on which the 

 despatches or other small parcels are trans- 

 mitted, has mounted upon it a small battery ; 

 and the ends of the coils are so adjusted that, 

 by means of the wheels and rails, the battery 

 connection is made successively with each of 

 the coils, just as the wagon is about to enter it. 

 The wagon itself being of sheet iron, it will be 

 attracted toward the middle part of each coil, 

 as the latter is thus made for the time to trans- 

 mit the current generated by the battery upon 

 it; and the momentum thus acquired by the 

 wagon in entering each of the coils is expected 

 to carry it far enough to make the connection 

 with the next coil, when the impulse and effect 

 are renewed. The suggestion of this device 

 appears to have been made by M. Bonelli. 

 Electric Sounding Apparatus. This appa- 



