112 



NATURE 



{May 30, 1889 



aggregate to 108. The burner is used without a glass chimney, 

 and thus there is no appreciable condensation pf the group of 

 flames, for their employment at the focus of optical apparatus, 

 and the relative aggregate intensity of the seven rings of flat 

 flames per unit of focal area, as compared with the four con- 

 centric flames of the old four-wick oil burner of Fresnel, is 

 only 2\ per cent, higher than the latter. The burner has five 

 powers, for varying states of the atmosphere. For the 

 minimum intensity, 28 jets are employed ; and with the whole 

 io8 jets there is a maximum aggregate intensity of the flames 

 with cannel gas of about 2500 candle units. Several 

 lighthouses on the coast of Ireland have been illuminated 

 with gas, on the system of Mr. Wigham, and two at 

 Haisborough, on the coast of Norfolk. In 1878, Mr, Wigham 

 installed at the Galley Head Lighthouse, County Cork, his 

 system of superposed gas flames, and group-flashing light, 

 which consisted of four of his large gas burners vertically super- 

 posed. In conjunction with these were four tiers of first order 

 annular lenses, eight in each tier. By successive lowering and 

 raising of the gas flames at the focus of each tier of lenses, 

 he produced his group-flashing distinction. This light 

 shows, at periods of one minute, instead of the usual single 

 flash from each lens, or vertical group of lenses, a group of short 

 flashes, varying in number between six and seven. The un- 

 avoidable uncertainty with this system in the number of flashes 

 contained in each group is unfortunate for the mariner, who, 

 with the continued increase in the number of coast lights, requires 

 the utmost precision in the distinctive character adopted for 

 each. 



In 1857, an experimental trial of the first magneto- electric 

 machine of Holmes, for the practical application of the electric 

 light, was made by the Trinity House at Blackwall, under the 

 direction and to the great delight of their scientific adviser, 

 Faraday ; and after a series of experiments the satisfactory 

 report of Faraday encouraged the Trinity House to order a 

 practical trial of a pair of the Holmes machines. The trial was 

 made at the South Foreland High Lighthouse by Faraday and 

 Holmes on December 8, 1858, when electricity was found to be 

 a formidable rival to oil and gas for lighthouse illumination, and 

 this position it maintains to the present day. The trials of this 

 arc light were made at the focus of the first order dioptric 

 apparatus for oil light, which was very imperfect for the purpose, 

 but they were sufficiently encouraging to lead the Trinity House, 

 under the advice of Faraday, to ]3roceed fiirlher with the electric 

 light for lighthouses. Faraday thus wrote in his report to the 

 Trinity House : — " I beg to state that, in my opinion, Prof. 

 Holmes has practically established the fitness and sufficiency of 

 the magneto-electric light for lighthouse purposes, so far as irs 

 nature and management are concerned. The light produced is 

 powerful beyond any other that I have yet seen so applied, and 

 in principle may be accumulated to any degree ; its regularity in 

 the lantern is great, its management easy, and its care, there 

 may be confided to attentive keepers of the ordinary intellect 

 and knowledge." 



These truly prophetic words of Faraday's have been entirely 

 realized. Electricity still stands foremost in the illumination of 

 our coasts, and appears destined to be one of the greatest 

 blessings ever conferred on humanity, and more especially on 

 "those who go down to the sea in ships." On February i, 

 1862, Holmes's machines and apparatus for electric Hj^ht were 

 installed at Dungeness Ligh ' house ; and in 1863, the French 

 lighthouse authorities followed, by an installation of the Alliance 

 Company's magneto-electric machines and apparatus for fixed 

 lights at each of the two lighthouses at Cape La Ileve. We 

 have here the fir t dioptric apparatus designed and manufactured 

 by Messrs. Chance Brothers and Co., of Birmingham, for the 

 electric fixed light at Dungeness. We have also one of the 

 Holmes lamps employed there. The lamp used at the previous 

 experiments was devised by M. Duboscq, of Paris. This lamp 

 of Holmes's is similar to those of Duboscq and Serrin, excepting 

 that the upper and lower carbons and holders are balanced and 

 regulated through pulleys and small catgut cords, instead of by 

 rack and pinions. The carbons are \ inch square, and the 

 mean intensity of the light in the arc was 670 candle units 

 nearly. We have here samples of the carbons employed 

 from time to time in the development of the electric light in 

 lighthouses ; we have also a Bergot lamp fitted with the fluted 

 form of carbons I have recently devised. They are of the 

 dimensions now in use in the optical apparatus at the St. 

 Catharine's Lighthouse, and are giving a mean intensity in the 



arc of 40,000 candle units (Fig. 5). Cylindrical compressed 

 carbons were soon manufactured for the electric light, and were 

 found to be more homogeneous in quality, and the flickering of 

 the light less, than with the original square carbons, which were 

 simply sawn from the residual carbon of gas retorts ; but there 

 was still the objectionable crater at the points, whether direct or 

 alternating currents were employed, involving flickering from 

 the incessant shifting of position at the points. A considerable 

 loss of radiant light was also involved, particularly when con- 

 densing it optically. The flickering was somewhat reduced by 

 an improvement of Messrs. Siemens', in providing the carbons 

 with a graphite core, but with the increasing powers of currents. 



and in the necessary dimensions of carbons, the results were far" 

 from satisfactory. With the fluted form of carbon shown on the 

 diagram, the formation of the crater is prevented, and the arc 

 is held centrally at the points of the carbons ; there is thus, in 

 addition to comparatively steady light, nearly uniform radiation 

 in azimuth, and over a greater vertical angle for optical condensa- 

 tion. It now appears to me, after some practical experience 

 with this form of carbon, that it is impossible to determine a 

 practical limit to the dimensions of carbons that may be effi- 

 ciently employed. With carbons of the actual size shown on 

 the diagram, an intensity of about a million candle units should 



