284 



ELECTKICITY. 



been taken not to let the arch strike the 

 single filament of silk which suspended the 

 talc. Having demonstrated that the talc was 

 repelled as described, the arch was allowed to 

 play against the silk fibre, which the author 

 expected would have been instantly burnt; 

 such, however, was not the case. Even when 

 a powerful induction coil replaced the bat- 

 tery, the fibre remained unhurt." 



Platinum Plates. In a paper read before 

 the Eoyal Society, Mr. 0. F. Varley notes the 

 various electrostatic capacity of platinum plates 

 immersed in acidulated water. With electric 

 potentials of less amount than sufficient to de- 

 compose water, these plates can be charged 

 and discharged like condensers. Mercury and 

 mercurial amalgams, he likewise found, could 

 be polarized with hydrogen. A vessel fixed 

 on a board has within it two funnels, con- 

 nected by tubes with two others outside. The 

 four are so arranged that, when each is about 

 one-third full of mercury, by tilting the board, 

 the mercury, in regaining its equilibrium, di- 

 minishes its surface in one of the funnels inside 

 of the vessel, increasing it in the other. The 

 vessel is then filled with acidulated water, and, 

 if the mercury is pure, no current takes place 

 on altering the relative surfaces; but, if one 

 surface is polarized with hydrogen and the bat- 

 tery removed, again augmenting the one sur- 

 face, and diminishing the other, an electric cur- 

 rent is set up. Mr. Varley could not succeed in 

 polarizing mercury with oxygen. By careful 

 measurement, he found that, with platinum 

 plates, the charge increases directly as the po- 

 tential up to 0.08 of a Daniell's cell, but beyond 

 that, that the charge increased in a much greater 

 ratio. He believes the variation is as the square 

 root of the potential ; and infers from his ex- 

 periments the impracticability of working un- 

 insulated telegraphic wires in the ocean. He 

 estimates that an uninsulated solid conductor 

 must be only 1,100 yards long to compete in 

 speed of signalling with 2,500 yards of the 

 same weight per mile of the same conductor 

 when insulated. 



Iron Electrotypes. In experimenting on the 

 production of iron electrotypes, M. Klein found 

 that the best results were obtained by placing 

 in the bath a plate of copper and uniting it with 

 the iron. The deposits became much more uni- 

 form, and, on reducing the energy of the cur- 

 rent, were highly satisfactory, until, finally, a 

 microscopic examination failed to detect any 

 porosity or irregularity in the deposits. 



On leaving the bath the iron is as hard as tem- 

 pered steel, and very brittle. Eeheated to a dull- red 

 heat, it loses much of its sharpness and hardness. 

 Heated to a cherry-red, it becomes malleable, and 

 may be engraved aa easily as soft steel. If the de- 

 posits are produced in good condition, and annealed 

 uniformly and with the necessary precautions, they 

 are neither subject to warp nor Dead. There is no 

 contraction, but, on the contrary, a slight degree of 

 expansion, almost imperceptible, however. Owing 

 to the necessity of having bank-note and similar 

 plates identical m every respect, it is of the first im- 

 portance that they should not be distorted nor have 



their dimensions altered in the process of annealing. 

 It appears that the galvanic deposit of iron has not 

 only permanent magnetism, but that, like soft iron, 

 it receives the magnetism of position. By replacing 

 plates of copper by those of iron, greater facilities 

 will be afforded for producing publications, works 

 of art, and especially bank-notes and checks. Iron 

 electrotype-plates are found to be almost indestruc- 

 tible. t They not only can be printed from an almost 

 unlimited number of times, but they are better cal- 

 culated than those of copper to withstand those in- 

 evitable accidents constantly occurring in printing- 

 establishments. Printers are sometimes obliged to 

 set aside as useless their best plates, which are often 

 damaged by a grain of sand, or by a chance knot in 

 the paper. These accidents not only involve the 

 expense of renewing the plates, but sometimes occa- 

 sion interruption and delays in works of a very press- 

 ing nature. These are some among the many which 

 may be expected to accrue from the introduction of 

 iron electrotypes. 



Electrotype^ Imitations of Leather. The 

 imitation of the choicest grains of leather 

 such as morocco and seal is now achieved on 

 a largo scale, at a Birmingham factory, at a 

 cost far below that of the actual skins. An 

 ordinary machine-roller is fitted up with a 

 mandrel, upon which is deposited by a new 

 process (not disclosed) a copper fac-simile of 

 the grain of leather to be imitated. The 

 Mechanics' Magazine says that an ordinary skin 

 can thus be impressed with the beautiful sur- 

 face of morocco, even to the finest variations 

 of grain, and several thousand may be copied 

 from one deposit. 



Dynamic Condensers. M. Saint-Edme, in his 

 new work on applications of electricity, speaks 

 thus of the dynamic condenser invented by 

 M. Garton Plant6: "It permits, so to speak, 

 of an accumulation of the powers of a battery 

 of two or three elements, until a discharge 

 equal to the force of fifty or sixty is obtained. 

 In ajar made with lateral grooves is arranged 

 vertically a series of parallel lead plates, very 

 close to each other, and perfectly insulated. One 

 series of pairs of plates is connected, and put 

 into connection with one of the poles furnish- 

 ing the current. The same is done with the 

 other series. The jar is filled with acidulated 

 water. The current of the battery decomposes 

 the water gradually, accumulating hydrogen on 

 one group of plates, and oxygen on the other. 

 If the two groups of plates are put into com- 

 munication, the oxygen and hydrogen combine 

 afresh, and produce a current of great inten- 

 sity. The action of the apparatus may thus 

 be indefinitely maintained. This condenser is 

 employed almost exclusively in surgery." 



Operating a Railroad ~by Telegraph. A 

 Denver (Colorado) correspondent of the New 

 York Tribune gives the following account of a 

 novel method adopted for the running of trains 

 by telegraph on the Denver and Kio Grande 

 Railroad: "The engineer alone has charge of 

 running the train. The conductor is an agent, 

 and he is also a telegraphic operator. Ho 

 carries a telegraphic apparatus with him, and 

 stations are attached to telegraph-poles being 

 little more than shelves and the agent com- 



