230 



NATURE 



\_yan. 9, 1879 



Mr. Valentin, Mr. Mellor, of Salford, and other friends, 

 my thanks are due for other substances. 



I have already pointed out that a large portion of the 

 •work done in the last four years has consisted in the 

 elimination of the effects of impurities. I am there- 

 fore aware of the great necessity for caution in the spec- 

 troscopic examination of various substances. There is, 

 however, a number of bodies which permit of the in» 

 quiry into their simple or complex nature being made 

 in such a manner that the presence of impurities will be 

 to a certain extent negligable. I have brought this 

 subject before the Royal Society at its present stage, 

 in the hope that possibly others may be induced to 

 aid inquiry in a region in which the work of one 

 individual is as a drop in the ocean. If there is 

 anything in what I have said, the spectra of all the 

 elementary substances will require to be re-mapped, and 

 re-mapped from a new standpoint ; further, the arc must 

 replace the spark, and photography must replace the eye. 

 A glance at the red end of the spectrum of almost any 

 substance incandescent in the voltaic arc in a spectro- 

 scope of large dispersion, and a glance at the maps pre- 

 pared by such eminent observers as Huggins and Thal^n, 

 who have used the coil, will give an idea of the mass of 

 facts which have yet to be recorded and reduced before 

 much further progress can be made. 



In conclusion I would state that only a small part of 

 the work to which I have drawn attention is my own. In 

 some cases I have merely, as it were, codified the work 

 done by other observers in other countries. With refer- 

 ence to that done in my own laboratory, I may here 

 repeat what I have said before on other occasions, that 

 it is largely due to the skill, patience, and untiring zeal 

 of those who have assisted me. The burthen of the final 

 reduction, to which I have before referred, has fallen to 

 Mr. Miller, my present assistant ; while the mapping of 

 the positions and intensities of the lines was done by 

 Messrs. Friswell, Meldola, Ord and Starling, who have 

 successively filled that post. 



I have to thank Corporal Ewings, R.E., for preparing 

 the various diagrams which I have submitted to the 

 notice of this Society. 



EXPERIMENTS IN ELECTRIC LIGHTING 



MR. LOUIS SCHWENDLER, Superintendent Elec- 

 trician of the Government of India, has been 

 conducting a very careful series of experiments in London 

 on electric lighting, with a view to decide upon the ad- 

 visability of introducing this method of lighting into 

 railway stations in India. He has just published 2i precis 

 of his forthcoming report, and as the experiments were 

 conducted on thoroughly scientific principles, and solely 

 with a view to discover the most effective method, the 

 results attained are extremely valuable, especially when 

 so many systems are competing for pubhc favour : — 



First, with regard to quantity of light per unit of power, 

 unit of speed, and unit of money (first outlay). To solve 

 this question Mr. Schwendler tried four different dynamo- 

 electric machines producing the electric current in one 

 direction, viz.. A, medium size, B, small ; as supplied by 

 Messrs. Siemens, Brothers, of London (construction : — 

 Siemens, system : — Hefner von Alteneck). C, workshop 

 pattern, as supplied by Messrs. Soutter and Lemonnier, 

 of Paris (construction : — Gramme). D, with two sets of 

 brushes as supplied by the British Telegraph Manufac- 

 tory (construction : — Gramme). Mr. Schwendler finds 

 these four machines all sufficiently practical for the pro- 

 duction of the electric light, but, as a rule, the statements 

 of their actual efficiency were not found to be in con- 

 formity with the results obtained from his own experi- 

 ments. The quantity of light produced by these dynamo- 

 electric machines had been over-rated, and the amount of 

 power consumed underrated. But, notwithstanding this. 



he finds that the unit of light as produced in the electric 

 arc (disintegration) by any of the four dynamo-electric 

 machines is at least fifty times cheaper than the unit of 

 light as produced by combustion, considering the expen- 

 diture of power only. This represents an enormous 

 engineering margin in favour of the electric light. 



Mr. Schwendler makes a most important proviso by 

 stating that this relation only holds good as long as one 

 dynamo-electric machine produces one electric light ; he 

 returns to this point in a subsequent part of his careful 

 precis. 



The three dynamo- electric machines B, C, and D, he 

 found practically equal; the dynamo-electric machine 

 A gives a much stronger light for a comparatively smaller 

 expenditure of power. In round numbers it may be said 

 that dynamo-electric machine A gives about double the 

 quantity of light given by any of the other three machines, 

 and that only about half as much power is expended to 

 produce the unit of light. This favourable result, Mr. 

 Schwendler states, is principally due to the comparatively 

 small internal resistance of A, and its low speed. 



Secondly, with reference to constancy and regularity 

 of the electric light, Mr. Schwendler says that this appears 

 to be still the weak point, and many improvements in 

 this respect are possible and desirable. He has tried 

 two different lamps : — a. The Serrin lamp, as supplied by 

 Messrs. Soutter and Lemonnier, of Paris, and the British 

 Telegraph Manufactory ; b. The Siemens lamp, as sup- 

 plied by Messrs. Siemens Brothers. The Serrin lamp, 

 for any given adjustment, regulates the length of the arc 

 only in one direction, i.e., it diminishes that length. The 

 actual consumption of the carbon points regulates the 

 length of the arc in the other direction, i.e., increases it. 

 In the Siemens lamp the decrease of the length of the 

 arc is effected exactly in the same manner as in the 

 Serrin lamp, but the increase in the length of the 

 arc is not only left to the consumption of the car- 

 bon points — a comparatively slow process — but is ac- 

 celerated by the addition of a make and break arrange- 

 ment, which separates the carbon points. Hence, from 

 a theoretical point of view, the Siemens lamp is un- 

 doubtedly superior, since the length of the arc is rapidly 

 adjusted in both directions, and consequently the working 

 currents can increase to a very considerable degree with- 

 out spoiling the dynamo-electric machine. But practi- 

 cally Mr. Schwendler finds the Siemens lamp somewhat 

 difficult to manage, and although, when once well ad- 

 justed, it burns as regularly as the Serrin lamp, it is far 

 more difficult to arrive at this adjustment. For practical 

 use he prefers, therefore, the Serrin lamp, with those 

 alterations and constructional improvements which his 

 own experiments have suggested. A second cause of the 

 irregularity of the electric light is the still imperfect state 

 of the carbon points. Of late some great improvements 

 have been made in the manufacture of artificial carbons, 

 but much more is required, and this point deserves the 

 closest attention. In his final report Mr. Schwendler will 

 treat this subject in detail. To make the electric light 

 more steady, Mr. Schwendler states, should be con- 

 sidered one of the most important questions to be solved. 

 Thirdly, Mr. Schwendler considers the question as to 

 how to put up the light, its position, and mechanical 

 details. Under this head he considers the method of 

 dividing the electric light, i.e. producing by the same 

 electro-motor a number of lights at different points of a 

 given space. This method, which he does not consider 

 as yet solved, appears to him impracticable from an 

 engineering point of view. He refers to the immense 

 loss of strength in thus dividing the light, increasing in 

 enormous proportion with the increase of sub-division. 

 Mr. Schwendler, after his careful, severe, and long- 

 extended trials, comes to the decided conclusion that the 

 electric light can alone compete with light produced by 

 combustion, when produced of great intensity in one 



