Sept. 13, 1877] 



NA TURE 



423 



of the carbon points, a great portion of which is due to 

 the combustion of the points in the air. M. Lodighin's 

 plan is to employ not two but a single stick of carbon, 

 inclosing it in a hermetically sealed glass chamber from 

 which all aii has been exhausted, and an azotic gas which 

 does not combine with carbon at a high temperature, 

 such as nitrogen, let in. When the current from a 

 magneto-electric machine, such as Wilde's, Gramme's, or 

 Noble's, is passed through this carbon it gradually gets 

 heated to a white heat, and emits a brilliant, and at the 

 same time soft and steady light. Fig. i shows the form 

 of the carbon used; the light is given off 

 at the narrow central part. The advantages 

 of this plan are that there is a continuous 

 circuit, so that any number of hghts may 

 safely be joined up in series to form one or 

 more lamps. The lights can bo made as 

 small as desired, the flame is continuous 

 and not injurious to the eye, the cost of 

 new carbon points is saved, and the current 

 can be strengthened or weakened at will 

 very easily. It burns equally well under 

 water, and would be very useful for illumi- 

 nating dangerous mines, there being no 

 fear of e.xplosion from it. One magneto- 

 electric machine driven by a 3 horse-power 

 engine, generates a light equivalent to 

 many hundred lanterns, and the light can 

 be easily divided up into smaller ones. 

 There was one defect in M. Lodighin's 

 original light which has been remedied by 

 M. Kosloff, of St. Petersburg. The unequal 

 expansion of the metal holder of the carbon 

 and the carbon itself caused the latter to 

 split and give way. The metal also fused, 

 and sparks passed between the carbon and the ex- 

 panded sockets. Kosloff fixed the carbon on insulating 

 supports of china, clay, crystal, &c., and connected it in 

 circuit by wires. The improved light of Lodighin and 

 Kosloff was first tried in London in 1874, and was very 

 successful. It was awarded the Lomonossow Prize by 

 the Russian Academy of Sciences. 



But the " electric candle " of M. Jablochkofif has, for the 

 nonce at least, quite cast Lodighin's light into the shade. 

 It appears to be one of those lucky inventions crowning 

 a long series of more or less unsuccessful ones in the 

 same direction. In the electric candle the two carbon 

 points are not dispensed with. They are placed side by 

 side and separated from each other by a slip of an insu- 

 lating substance such as porcelain, brick, magnesia, but 

 preferably kaolin or pure clay. One of the points is a 

 little longer than the other, and may also be stouter. The 

 positive current is passed down the longer carbon, and 

 leaps across the air space to the shorter carbon, forming 

 the luminous arc at the point of the candle. Such an 

 arrangement of the points is shown in Fig. 2. It is called 



Fio. 1. 



gia . ^^ 



liaoJiyte 



Fie. 2. 



a candle because it can be burned upright in a support 

 like a candlestick. The kaolin plays an important part 

 besides insulating the carbons from each other. It 

 becomes incandescent, emitting a beautifully soft, steady, 

 light, and melts away like wax at the same rate as the 

 carbons, just as a candle is consumed with the wick. No 

 mechanism is required for the adjustment of this electric 

 candle. The discovery that kaolin becomes intensely 

 incandescent under the current also enables M. Jabloch- 

 koff to dispense with the carbon points for small and 

 medium hghts. He made the discovery, we believe, in 

 studying the effect of a succession of sparks from the 

 secondary coil of an induction machine on refractory 



bodies. He first heated a plate of kaolin to incan- 

 descence, but did not fuse it. Then he led the induc- 

 tion current along the edge of the plate by means of a 

 more conductive coating. This caused the edge to fuse 

 and emit a splendid band of light as soft and steady as 

 any known source. This discovery disclosed a feasible 

 system of lighting towns and dwelhngs by dividing the 

 electric light. It would be possible to generate lights of 

 all sizes by means of the kaolin ; and by employing a 

 number of separate secondary coils, one to each candle, 

 for one primary, the current could be simply and 

 effectively divided. By having the carbon candles for 

 large ware'iouses and public buildings, and a very simple 

 pincher holding a kaolin wick for offices and corridors ; 

 and by having separate secondary circuits to each set of 

 lights, electricity could be laid on for illuminating pur- 

 poses as easily as gas. The passage of the current 

 through the kaolin makes the circuit complete as in 

 Lodighin's plan, and a number of lights can be joined up 

 in the same circuit, so as to form a set of luminous 

 centres. As many as eight candles have been kept 

 steadily burning in the circuit of an ordinary magneto- 

 electric machine. Some of the principal halls of the 

 j Louvre have have been lighted by the candle in this 

 way. MM. Denayrouze and Jablochkoff have, we are 

 told, easily obtained fifty luminous centres of various 

 intensity in graduated series, the weakest yielding a glow 

 equivalent to one or two gas burners, the strongest equal 

 to fifteen burners, from one current. By eipploying a 

 magneto-electric machine giving alternating currents the 

 current interrupter and condenser of the induction coil 

 may be dispensed with, the alternating currents being 

 simply passed through the primary coil. Again, by 

 employing a magneto-electric machine yielding several 

 powerful intermittent currents, the induction coil with its 

 several secondary coils may be dispensed with altogether 

 and the magneto-electric currents passed through the 

 candles. This power of being able to divide up the 

 current so as to have several circuits with several candles 

 of various degrees of illuminating effect in the same 

 circuit, or only one, gives to electric lighting the con- 

 venience of gas. It cannot be so expensive as gas, and it 

 must be far less pernicious and dangerous than gas in a 

 house. The lights require to be shaded by ground or 

 opal glass shades to diffuse the rays. The consumption 

 of kaolin is very small. It is said that a piece the length 

 of a centimetre will last ten hours. 



The recent public trials of Jablochkoffs light at the 

 West India Docks have been recorded in Nature. The 

 first was unsuccessful owing to some defect in the magneto- 

 electric apparatus. An account of the second and success- 

 ful trial was given in Nature, vol.xvi. p. 153. A large tent 

 inclosing 900 squaie feet was illuminated by four candles 

 fixed on lamp-posts and surrounded by globes of opal 

 glass. At twenty or thirty feet from the lamps very faint 

 pencil hues could be distinguished on paper, and small 

 print read at a considerable distance. When common 

 candles were substituted for the electric lights the effect 

 was most marked, and the light a sickly yellow. In the 

 electric illumination the most delicate colours retained 

 their purity of tint. A warehouse was also lighted up by 

 three naked candles ; and a ship lying alongside a wharf 

 by two, in order to show that lading or unlading could be 

 carried on at night. J. Munro 



REDUCTION OF THE HEIGHT OF WAVES 

 BY LATERAL DEFLECTION UNDER LEE 

 OF BREA KIVA TERS 1 



WHEN a wave encounters an obstacle such as a 

 breakwater, the portion which strikes it is either 

 entirely destroyed or reflected seawards, while the portion 

 which is not so intercepted passes onwards, and spreading 



» By Thomas Stevenson, F.R.S.E. 



