202 



NA TURE 



{June lo, 1887 



Chance. It is, above all, to Sir James Douglass that 

 credit is due in this field. For at least eighteen years he 

 has worked unweariedly, and in the interest of the public 

 service alone, at the perfecting of the burners which bear his 

 name, whether for colza, paraffin, or gas ; and some striking 

 developments have been attained by him. For instance, 

 the typical four-wick vegetable-oil burner of Fresnel had 

 an intensity of 230 candle-units, or 23*6 units per square 

 inch of sectional area. The Trinity four-wick has an 

 intensity of 415 candle-units, or 44"3 per square inch. 

 The Trinity six-wick, perhaps the most serviceable and 

 complete burner ever constructed, equals 730 candles, or 

 40' I per square inch. The Trinity seven-wick equals 

 1 100 candles, or 46'9 per square inch, and the Trinity 

 nine-wick equals 1785 candles, or 49"8 per square inch. 

 These burners are all for vegetable or mineral oil. The 

 Trinity six-ring gas-burner equals 853 candles, or 44*4 per 

 square inch ; and, which appears to be the most powerful 

 combina'tion ever attained, the Trinity ten-ring gas-burner 

 reaches 2619 candles, or 50*9 per square inch of sectional 

 area. The admirable expanding gas-burners of Mr. 

 WigJiam are hardly less powerful. They are formed of 

 concentric circles of jets from 28 to loS in number, dis- 

 posed so as to suit optical apparatus of several degrees of 

 size, and weather of every degree of clearness. To this 

 gentleman must be accorded the same pre-eminence in 

 the skilful use of gas for lighthouses as to Capt. Doty 

 for the skilful use of mineral oil. His ingenious combina- 

 tions and contrivances, not only in regard to power, but 

 to distinctiveness of character, are seen to great advant- 

 age in Galley Head and other notable Irish lights. It 

 has been urged against gas flames of the largest dimen- 

 sions on this system, that a portion of light escapes 

 lenticular action, yet this very ex-focality has been found 

 to have a useful side, for it tends to produce a glare or 

 glow in the heavens, visible to mariners when the tower 

 is beneath the horizon, and, in some circumstances, posi- 

 tively useful to them. (The electric light produces a 

 similar elifect, though in a different manner.) A more 

 serious objection to large gas flames, especially when 

 used in triform or quadriform series, appears to be the 

 excessive heat, which is capable of injuring the delicate 

 optical glass, and is hardly favourable to the keepers. It 

 is probable that the hyper-radial apparatus just introduced 

 may, both as relates to condensation of light and to mitiga- 

 tion of heat, be well suited to gas-burners of these striking 

 magnitudes. Of the thirty-two dioptric sea-lights in Ire- 

 land, about one-fourth are successfully endowed with the 

 gas-illuminant. Of the sixty-five in England, the Hais- 

 boro' is the only case. There is no gas in the fifty-one 

 Scottish sea-lights, except Ailsa Craig, which has oil-gas. 

 It should be added that the compressed mineral-oil gas of 

 Messrs. Pintsch,and the petroleum spirit of H err Lindberg, 

 for the automatic lighting of buoys, have been, since 1878, 

 tried in this country with great success. 



The third illuminant, electricity, has been known in 

 England for about thirty-five years. As generated in the 

 magneto-machines of Prof. Holmes between 1853 and 

 1862, and as tried experimentally in the lighthouses of 

 Dungeness and South Foreland, it was very small in 

 dimension and very uncertain in character. Several 

 forms of the light were suggested during this period, such 

 as the voltaic arc of Watson and the mercurial electric 

 lamp of Way. With the more effective alternating cur- 

 rent machines, and with the larger carbons, of later years, 

 the arc grew in power and dimension. At the present 

 time carbons of from 25 to 40 millimetres are available, 

 with an intensity in the focus of a light of ten times that 

 of the most powerful gas or oil burner. The arc is thus 

 become a most valuable resource, not merely for its un- 

 surpassable power, but also for its focal adaptability to 

 the usual ;_dioptric apparatus, and to special optical com- 

 binations dictated by nautical circumstances. It is most 

 flexible in its application. It radiates no harmful heat 



It has the high merit of not exacting any abnormal 

 dimensions of apparatus, lantern, or tower. Lastly, being 

 the most powerful in all its gradations relatively to other 

 illuminants, it is the cheapest of all lights if the cost of 

 establishment and maintenance be computed in terms of 

 the units of the beam transmitted, which is the only 

 strictly logical and practical way of treating it. For 

 these reasons it has been chosen in France as the best 

 illuminant for a large number of coast-lights, and it is 

 making rapid way in Europe and America. It may 

 therefore be safely asserted that the electric light, when 

 it shall have been freed from its last disabilities, and 

 shall have attained its utmost development, will, in the 

 not distant future, be the prevailing illuminant of our own 

 lighthouses and of the other chief lighthouses of the world. 



In illustration of the power of the electric arc with 

 suitable optical treatment, I may mention that the direct 

 beams of the Tino light, near Spezia, were observed on 

 April 20, 1885, by Prof Noceti, from the hill S. Giorgio, 

 behind Savona, at an elevation of 2733 feet, and a distance 

 of 73 statute miles, the atmosphere being clear and under 

 moonlight. The beams of the arc were notably brighter 

 than those of the lavierna at Genoa, at one-third of the 

 distance. Frequent observations are reported of the 

 Macquarie light in New South Wales, at ranges of 60, 

 65, and 70 nautical miles, by means of reflections on the 

 sky while the light itself is below the horizon. 



The relative merits of gas, oil, and electricity, were 

 established in the prolonged official experiments at the 

 South Foreland in 1884-85. It has been proved that 

 there is no appreciable qualitative difference between 

 mineral oil and coal-gas as light-giving agents ; and that 

 such differences as appeared were rather quantitativCy 

 arising from the number and dimensions of the burners, 

 and the modes of their collocation or superposition. It 

 has been proved also that the electric arc (in addition to 

 its superiority in clear weather, which was never in ques- 

 tion) has an absolute superiority in thick weather to both 

 gas and oil — "the greatest penetrative power in fog." 

 Much public controversy has been excited by the Report 

 in which conclusions like these are embodied. The 

 fairness and impartiality of persons concerned in the 

 investigation have even been impugned, and objection 

 has been taken to the manner in which the electric light 

 was presented to the observers, and to the refusal of the 

 Trinity House to accept certain maximum arrangements 

 called " double-triform " and " double quadriform." But 

 to anyone reading the Report of the Trinity House (1885) 

 with no bias toward a particular interest or a pre-con- 

 ceived theory, it must appear that the inquiry was as 

 exhaustive as it was prolonged, and that it is impossible 

 that such names as those connected with it^names 

 eminent in science, in engineering, and in the nautical 

 and official world — should be associated with any other 

 desire than the desire to shed light on a vexed technical 

 question, and to achieve honourably and thoroughly a 

 great public work. With regard to the exclusion of 

 maximum combinations from the Foreland pi-ogramme, 

 it was obviously sufficient to compare gas and oil in 

 their respective primary burners, multiplied or combined 

 in such a way as, while insuring equal terms or nearly 

 so, to reproduce the actual or allowable conditions of 

 a lighthouse ; and nothing would seem to be gained by 

 augmenting the rival elements pari gradu to ampler and 

 ampler bulk regardless of all else. The inter- I'elation of 

 the numbers one, two, three, is not affected, or very 

 slightly so, by raising them to two, four, six, or to four, 

 eight, twelve. And although the highest power of the 

 initial flame or the emerging beam were reached accord- 

 ing to the opinion of the moment, the next day might 

 suggest a still higher power, until it became clear that we 

 might as well revert to the old beacon-fire on the head- 

 land, for indeed with unlimited tar-barrels or profuse 

 pine-logs a light cottld be kindled exceeding everything 



