ELECTRICITY. 



275 



Ingeniout Electrical Experiment*. A coarse 

 of seven lectures, delivered by Prof. Tyndall, 

 at the Royal Institution during the summer, 

 were illustrated by many novi-1 ami highly- 

 ingenious experiments, such as the following: 

 The elongation of a solid bar of iron, when it 

 is thrown in the magnetic state by being en- 

 riivled in the folds of a voltaic current, con- 

 veyed by a helix, was shown by the starting 

 of a spot of electric light some or 8 inches on 

 a -riven, when the molecular condition of mag- 

 netism was excited by the passage of the cur- 

 rent. The change in the position of the mol- 

 ecules of iron was proved by throwing the 

 beam of light through a vertical cell of glass 

 containing magnetic oxide of iron suspended 

 in \\ liter. An artificial telegraph-cable, whose 

 resistance to the transmission of the electrio 

 current was made identical with 14,000 miles 

 of an actual marine cable, was formed by intro- 

 ducing, into the path of the current, gaps, con- 

 sisting of feebly-conducting liquids and con- 

 densers, so distributed as to represent the 

 respective distances, by telegraphic routes, of 

 Gibraltar, Malta, Bombay, Australia, and many 

 other places. Before the current was sent 

 through this line, dots of light, one for each 

 station, cast from mirrors by the instrumental- 

 ity of electric illumination, lay upon the screen 

 in a straight vertical range. When the current 

 was passed, dot after dot started aside upon the 

 screen, the movement of the dots indicating 

 the points successively reached by the current, 

 the interval of time between each representing 

 the interval that would actually occur in tele- 

 graphing between the real stations. Another 

 interesting beam-of-light illustration is the one 

 employed to indicate the excitement of dia- 

 magnetic force in a tube of copper suspended 

 between the poles of an electric magnet. The 

 tube is carried by a string of silk, and rotates 

 rapidly when the string is touched. The same 

 string also carries above the tube a series of 

 small mirrors which reflect the light of an 

 electrio beam, so that a continuous elliptical 

 band of illumination is formed on the screen 

 while the twisting is continued. The instant 

 the electro-magnet is made active by the 

 transmission of the current through its helix, 

 the copper tube acquires diamagnetic polarity 

 by induction, and under the influence of this 

 polarity the rotation is arrested, and the band 

 of lights upon the screen is changed into a 

 small stationary spot of illumination. "When 

 the electro-magnet is unmade by the arrest of 

 the voltaic current, the spot of light again be- 

 comes an elliptical band, under the resumption 

 of the twisting of the silk string with its mir- 

 rors and copper tube. The sound produced by 

 the molecular vibration in iron, when its mass 

 is transiently magnetized by the voltaic cur- 

 rent, is made audible by suspending an iron 

 poker upon two sounding-boards, and making 

 it the core of a helix, conveying an electrio 

 current. An assistant is converted into an 

 extemporized electrophoros, by flapping his 



black coat with fur while he stands upon a 

 glass-legged stool. Small fish of gold leaf are 

 made to float in the air-current given off from 

 the knob of a charged Leyden jar. To de- 

 monstrate the relation of resistance to heat- 

 ing power, a long line of wire is arranged 

 in alternate links of platinum and silver, and, 

 when a voltaic current of due intensity is 

 passed through the length, each stretch of the 

 platinum wire is seen to glow with brilliant 

 red heat, while the stretches of silver wire be- 

 tween remain still invisihlc. A beautiful series 

 of Geissler's vacuum-tubes was brought into 

 successive operation, in which the auroral dis- 

 charge was broken into stratified leaves, in 

 which the glow was extinguished by the ap- 

 proximation of the poles of an electro-magnet, 

 in which a feeble glow was converted into 

 bright stratified light by the influence of a 

 magnet ; and, beautiful beyond all the rest, the 

 light from the enclosed negative terminal of 

 the voltaic battery was arranged into the well- 

 known lines of magnetic force, when subjected 

 to the influence of the poles of a magnet. 



New Forms of Battery. 31. Figuier has 

 devised a cheap battery on the principle of 

 Smee's. He makes plates of retort-coke, paints 

 them with a strong solution of chloride of 

 platinum, dries them, and then reduces the 

 chloride on the coke by heating it in the fire, 

 leaving the coke coated with metallic platinnm. 

 Silvered carbon may also be used, but that is 

 obtained with more difficulty. Either of these 

 kinds of plates the inventor thinks superior to 

 those used in a Smee's battery, the irregular 

 surface of the former preventing the escape of 

 hydrogen. He gives a rough surface to the cut 

 plates of retort-coke by spreading them over 

 with a mixture of diluted white of egg or 

 blood-albumen and syrup, and then carefully 

 burning them until smoke is no longer given 

 off. This process being repeated two or three 

 times, myriads of points, the debri* of minute 

 vesicles, remain firmly attached to the original 

 carbon plates. The plates thus made must be 

 well washed in a large quantity of water, to 

 remove any loose particles which might other- 

 wise fix themselves accidentally upon the zinc, 

 and set up local action. They are said to last 

 in use at least three years. 



Delavosier has contrived a battery capable 

 of producing a very regular current without 

 amalgamating the zinc, and evolving no gas. 

 It consists of a galvanic cell, composed of zinc 

 and carbon, placed in a fluid made up of 40 

 parts water, 4.5 parts bichromate of potash, 9 

 parts concentrated sulphuric acid, 4 parts sul- 

 phate of soda, and 4 parts double sulphate of 

 potash and iron. 



Nature speaks approvingly of Mr. J. Parnell's 

 new secondary battery. It is so constructed 

 as to do a large amount of heavy work, having 

 forty cells, each containing a pair of copper 

 plates immersed in a solution of the impure 

 carbonate of sodium, known in commerce as 

 " soda." By this employment of an alkali, the 



