52 



NATURE 



[Nov. 2 1, 1878 



LETTERS TO THE EDITOR 



[The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, or 

 to correspond with the zvriters of, rejected manuscripts. No 

 notice is taken of anonymous co?nmunications. 



[The Editor urgently requests correspondents to keep their letters as 

 short as possible. 77ie pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting and novel facts.l 



The Divisibility of the Electric Light 



^ The English and American periodicals devoted to electrical 

 science now announce, " on authority," that the electric light 

 discovered by Edison is a light by incandescence. If this be 

 true there is nothing new or startling either in the discovery of 

 the light or of its divisibility. Lighting by incandescence has 

 been studied for a long time ; indeed, it has been studied much 

 more thoroughly than any other kind of electric lighting. Thirty- 

 three years ago a method of producing and sub-dividing the light 

 was patented in England by a Mr. King. The light was pro- 

 duced by heating to white heat in a vacuum, by means of the 

 electric current, either platinum or carbons ; and, the specifica- 

 tion adds, ' ' when the current is of sufficient intensity, two or a 

 larger number of lights may be placed in the same circuit." For 

 some years after this discovery several improvements on King's 

 invention were patented in America, France, and England ; 

 "but," says M. Fontaine, "none of these appear more complete, 

 more explicit, and more practicable than King's ; it is, then, 

 useless to continue our nomenclature. " The principle of lighting 

 by incandescence, although not neglected or forgotten, seems to 

 have made but little progress until 1871, when M. Lodyguine 

 showed an experiment in the Admiralty Dockyard in St. Peters- 

 burg, when he divided the circuit into no less than two hundred 

 lights. This natui-ally made a great sensation at the time — as 

 great a sensation as that caused by Mr. Edison's telegram of the 

 7th ult. The Academy of Science awarded to M. Lodyguine 

 the large Lomonossow prize of 50,000 roubles. A company was 

 formed in St. Petersburg with a capital of 200,000 roubles, and 

 the excitement in Europe was then almost as great as has been 

 witnessed in England lately. It was soon found, however, that 

 Lody^uine's discoveries, like those of his predecessors in the 

 same field were, after all, impracticable, and that his illimitable 

 division of the light, however ingenious, was only a fanciful 

 experiment. Every penny subscribed to the company referred 

 to was lost, and Lodyguine's great discovery is now, where it 

 was then — in his laboratory. 



It has, however, been urged "that 'these 'early inventors of the 

 electric light knew only of the galvanic battery as a generator of 

 a powerful current, and that had they known of the Gramme 

 machine, or other dynamo- or magneto-electric machine, the 

 results might have been different. The remark, however, only 

 applies to King and the improvers who immediately succeeded him. 

 The great division of the light by Lodyguine, to which reference 

 has just been made, was in a circuit produced by two " Alliance" 

 »nachines. Even, however, if such were not the case, there are 

 at present before the world, in more or less detail, four recent 

 inventions for the production of a divided light by incandescence. 

 These are the inventions of M. Reynier, of M. Arnaud, of Mr. 

 Edison, and most recent of all, M. Werdermann. From the 

 way in which these discoveries — if they are discoveries — have 

 been ushered into the world, it is found that great claims are 

 made on their behalf, and there are, therefore, naturally great ex- 

 pectations on the part of the public in regard to them. It cannot 

 be urged now in mitigation of the shortcomings of the incan- 

 descent light, as it has been urged in the past, that it has not had a 

 fair trial, on the ground that the lamps in existence were im- 

 perfect in conception, and complex in construction. The lamp 

 of M. Reynier seems admirable in its way, and if light by 

 incandescence were to be the light of the future, the claims of 

 this lamp would have to be very carefully considered, and, in 

 any ca-e, it will certainly hold an important place in all investi- 

 gations into the subject. The lamp of M. Werdermann appears 

 to be identical in principle with, and only slightly different in 

 detail from, that of M. Reynier, and we may fully expect that 

 the>e inventors will have to come to terms with each other — so 

 much alike are their inventions. Of the details of Mr. Edison's 

 invention — if there are any, nothing is known beyond the fact 

 stated in the Scientific American, that it is a light produced from 

 a spiral of incandescent platinum ; while the reports in the 

 American daily press show such an effervescent ignorance of the 



fundamental principles both of electricity and of dynamics, that 

 no reliance whatever can be placed upon them. 



Experience, then, has shown that a light by incandescence 

 comes before us in a very questionable shape, and it is essentially 

 a light which discourages the notion of its practical application. 

 The question indeed may be very properly asked : How is it that 

 light by incandescence has always provedjsuchan utter failure? 

 It has had a period of thirty-three years in which to develop ; 

 it has been divided into various lesser lights, numbering from 

 two to two hundred : and it has arrested the attention and taxed 

 the skill of the greatest electricians in the world. How is it that 

 it is obliged to give way to light by the voltaic'arc ? The answer 

 is at hand. The light by incandescence can only be obtained and 

 divided by a great sacrifice of light and power. This is impera- 

 tive from the fundamental principles of electrical science. The 

 diminution according to the "square," and not according to 

 simple proportion, applies to electricity just as it applies to light, 

 heat, sound, gravitation, and other physical phenomena. Thus 

 if a circuit be divided into two branches whose resistances are 

 equal, a current of half the strength passes through each branch, 

 producing at the point of resistance, not half the light, but only 

 a quarter, because the effect follows the square of the current 

 strength. If the current had been divided into three equal 

 branches, in each branch only one-ninth part of the original 

 light would be obtained, and so on ; so that if an electric light 

 of 1, 00c candles were divided into ten equal lights, the result 

 would be ten lights of ten candles each, instead of one of i,ooa 

 candles. When this law is borne in mind, and when it is also 

 remembered that to produce the electric light by incandescence 

 at least one-half of the current is lost, it will easily be imagined 

 what a wasteful hght it is. Recent experiments prove this. It 

 was recently stated, in reference to M. Werdermann's incan- 

 descent light, that he produced two lights of 320 candles each 

 (total, 640 candles), with a prime mover of 2 horse-power ; and 

 this was considered a great result — as indeed it was for an incan- 

 descent light. But how this sinks into insignificance when com- 

 pared with the results of lighting by the voltaic arc. A few days 

 ago M. Rapieff", with two of his regulators and a small Gramme 

 machine known as the M machine, and which M. Gramme says 

 requires only l§ horse-power, produced two lights, which, when 

 carefully measured by the photometer, were found to be ' each 

 equal to i, 150 candles, or a total of 2,300 candles, while with one 

 of M. Gramme's A machines, requiring 2| horse-power, a light of 

 6,000 candles can be obtained from one of M. Rapieft's regu- 

 lators. Some experiments detailed in M. Fontaine's book on 

 " Electric Lighting " gave a similar result. M. Fontaine's ex- 

 periments with an incandescent light show that, under the most 

 favourable circumstances, with a Bunsen battery of forty-eight 

 cells, eight inches high, the diminution of the sub-divided light 

 was so great that, where he put five lights in one circuit, he only 

 obtained a total illuminating power of a quarter of a burner, 

 with four lamps only three-quarters of a burner, with two lamps 

 six-and-a-half burners, and with one lamp fifty-four burners. 

 These numbers give the following ratio : i, 3, 8, 26, 216, thus 

 showing how rapidly the light diminishes when divided. With 

 the voltaic arc, however, and with the same battery, he was 

 able, by a Serrin lamp, to obtain a light of 105 burners. 



It will be seen, then, from what has been above stated, that 

 the production and the divisibility of the light by incandescence 

 is a very wasteful process — so wasteful, indeed, as to render its 

 practical application impossible for general lighting. If, there- 

 fore, all Mr. Edison has to announce to the world is that he has 

 succeeded in dividing an incandescent light — and the announce- 

 ment that such is so is made on authority — his discovery amounts 

 to very little. Both the light and its divisibility were discovered 

 long ago. It will easily be seen that it is not in that direction 

 that any great practical results can be obtained. The voltaic 

 arc supplies the only divisible light of any utility and economy, 

 and it is in its development that any real progress must be looked 

 for. William Trant 



Duplexing the Atlantic Cable 



I HAVE read with surprise in your number of the r4th inst. 

 (vol. xix. p. 38), an article, in which it is implied that the 

 application of the duplex method of signalling to an Atlantic 

 cable has now for the first time been successfully accomplished 

 by Mr. Stearns. 



The publication in the Times of Sir James Anderson's letter 

 on " the duplex system in telegraphing," on the day after the 

 publication of your article, was a coincidence of which I trust 



