Dec. 2, iS8o] 



NATURE 



105 



that created two years ago by the far less formidable 

 experiments of Mr. Edison in the same direction. 



The material which Mr. Swan proposes to render in- 

 candescent by means of an electric current is a "wire" 

 of prepared.carbon of extraordinary density and elasticity. 

 Twenty years ago he prepared carbon filaments for 

 the very same purpose from calcined cardboard, in. 

 closing them in a glass vessel from which the air 

 was withdrawn as perfectly as the imperfect air-pumps 

 of that date permitted. In October 1877, or one year 

 before Mr. Edison had begun to attempt the con- 

 struction of lamps with carbonised paper, Mr. Swan 

 had some prepared carbons mounted in glass globes and 

 exhausted by the Sprengel air-pump by Mr. Steam of 

 Birkenhead. This enabled Mr. Swan to discover that 

 when the carbon was properly fixed and heated during 

 exhaustion so that the occluded gases might be ex- 

 pelled, there was an end of the causes that hitherto had 

 seemed to defeat all attempts to utilise this method of 

 procuring an incandescent electric light ; for when these 

 conditions were observed there was none of the disin- 

 tegration of the carbon rods, nor of the blackening of the 

 globes that with less perfect vacua had proved the ruin of 

 carbon lamps. The filaments of carbon now pro- 

 duced by Mr. Swan indeed resemble steel wire rather 

 than carbon, so extraordinary is their tenacity and 

 texture. The secret of their manufacture has not 

 yet been made known, being the essential point of 

 the patent rights which Mr. Swan has just secured. 

 Each filament is about three inches long, and not 

 more than the hundredth of an inch in diameter, and is 

 so slight as only to weigh fronr one-fifteenth to one- 

 twentieth of a grain. The durability of these filaments 

 is remarkable. In the course of a lecture delivered on 

 November 25 last before the Society of Telegraph Engi- 

 neers, Mr. Swan stated that he had had lamps lighted 

 continuously since August 30, with an intermission of 

 three weeks only, and that this seemed to be far from the 

 actual limits of durability. When the currents employed 

 are not too strong, the lamps will last longer. The light 

 yielded by these lamps varies, according to circumstances, 

 from thirty to fifty standard candles. On the occasion of 

 Mr. Swan's lecture thirty-six of these tiny lamps were ex- 

 hibited working by the current of a dynamo-electric 

 machine requiring four horse-power to drive it. In the 

 debate which followed Mr. Swan's communication, the 

 remarks made by Prof. Tyndall, Dr. Hopkinson, Mr. 

 Alexander Siemens, and others, showed the real value 

 of the advance made by Mr. Swan. The question 

 however of the economy of the system remains yet to be 

 decided by the practical test of durability. At a previous 

 lecture at Newcastle-on-Tyne Mr. Swan exhibited twenty 

 lamps fed by a current generated by a gas-engine con- 

 suming 160 cubic feet of gas per hour. The light obtained 

 exceeded that of the seventy gas-jets which usually sup- 

 plied the same room, and which consumed 280 feet per 

 hour. Mr. Swan proposes to connect these lamps in series 

 of fifty or a hundred in one circuit, using automatic circuit- 

 closers to close the circuit in the rare case of the failure 

 of a lamp. He considers his method of arranging the 

 system to be superior to that proposed by Mr. Edison, 

 whose method of placing the separate lamps in single 

 branches of a divided circuit would involve the use of 

 very heavy and costly conducting-wires without any 

 counterbalancing advantage. With this important differ- 

 ence Mr. Swan's further proposal to erect central stations 

 from which to supply currents of electricity over large 

 areas resembles that suggested by INIr. Edison. Should 

 the anticipations of the inventor and the present promise 

 of the new lamps be fulfilled, domestic electric lights will 

 certainly become a fact at no distant date. 



Meantime Mr. Edison has not been idle. It is stated 

 that he is at present laying down a service of about seven 

 miles in length upon which to test the success or failure 



of his system upon a largo scale. He has developed 

 several ideas since his last appearance before public 

 notice. He now makes his dynamo-electric generators 

 of a much larger pattern than any heretofore attempted. 

 He has abandoned charred cardboard in favour of a 

 filament of carbon prepared from a cultivated variety of 

 the Japanese bamboo. We shall hear before long whether 

 his indomitable perseverance has been rewarded with 

 final success. In spite of being in point of date behind 

 i\Ir. Swan, he has the enormous advantages of a unique 

 workshop and laboratory under his own direction, of a 

 wealthy company at his back, and of the extraordinary 

 prestige won by his previous inventions. If Mr. Swan 

 appears to be nearer to a genuine success, Mr. Edison 

 has a popular reputation that of itself will win a hearing for 

 the most trivial of his inventions. Whichever of the rival 

 systems succeeds science and mankind are the gainers. 

 But up to the present point it seems to us that beyond 

 question Mr. Swan is nearer the goal of practical results 

 than his famous rival. 



It may interest our readers to know that Mr. Edison's 

 first carbon lamp is now on view along with his original 

 phonograph and his earliest tasimeter in the Patent 

 Museum at South Kensington. 



SUBTERRANEAN FOREST IN INDIA 

 'T'HE accompanying notes and illustrations on the 

 -'• underground forest recently discovered in exca- 

 vating the Prince's Dock, Bombay, were forwarded by 

 Col. C. J. Merriman, R.E., C.S.I. , Member of the Legis- 

 lative Council, and Secretary to Government (Public 

 Works Department), Bombay. 



The trees were generally found in a dark loamy soil 

 composed of underlying rock disintegrated. The upper 



portion of the trunks stopped at the soft black clay, 

 which is silt. A few went a little way beyond ; but as far 

 as they protruded into the silt they were completely 



•^i/rfdce of CrCJnd 



Fig. 2.— Section in line of trees B to F. Scale ,'5 inch to i foot. 



riddled by the teredo, the nearer the root the bigger the 

 hole, showing that the boring began from the top. 



The roots of the highest tree found were at 72-20 on T.H. 

 datum, or close on Low Water extreme springs, about six 

 feet under the surface of the mud. The lowest root was 



