436 Sir James N. Douglass [March 15, 



nation ; but owing to the imj^erfect refinement of the best samples of 

 the latter then procurable in the market, together with its high price, 

 the result of the investigation was not so satisfactory as to justify a 

 change from colza. In 1869 the price of mineral oil of good illumi- 

 nating quality and safe flashing point, was found to be procurable at 

 about half the j)rice of colza, when the Trinity House determined to 

 make a further series of exj)eriments, and by these it was ascertained 

 that, with a few simjDle modifications of the Argand burners then in 

 use, they were rendered very efficient for the purpose, it was also 

 found tliat these burners were thus considerably improved for the 

 combustion of colza. A change from colza to mineral oil was then 

 commenced, and mineral oil is now generally adopted in the light- 

 houses and light-vessels of the Trinity House service, and with even 

 greater economy than was at first anticij^ated ; the price of this 

 illuminant being now rather less than one-third that of colza. The 

 most powerful oil burner then in use was one of four concentric wicks, 

 the joint production of Arago and Fresuel, and adopted by the French 

 lighthouse authorities about the year 1825, in conjunction with the 

 then new diojjtric system of optical apparatus of Fresnel. The 

 standard intensity of the combined flames of this burner, one of 

 which we have here, was 260 candle units. A farther development 

 was made, during the experiments of the Trinity House in 1871, by 

 increasing the number of wicks from four to six, which more than 

 doubled the intensity of the light, while effecting a condensation of 

 the luminary j^er unit of focal area, or in other words improved the 

 optical efficiency 70 per cent. We have here also one of these burners. 

 I have since devised an Argand burner for the combustion of all 

 illuminating gases and oils, whereby still further condensation of the 

 flames, together with greater intensity and economy of combustion, is 

 obtained, and the glass chimney is protected from breakage. These 

 imj^rovements are efi'ected by a special arrangement and distribution 

 of the air currents through the rings of flame, and between them and 

 the glass chimney. (See Models.) We are thus enabled on this system 

 to increase the dimensions of lighthouse burners, for gas and oil, for 

 ten or more rings of flame. With ten rings we obtain an aggregate 

 intensity, when burning cannel gas and good mineral oil, of consider- 

 ably over 2000 candle units, while the improved efficiency of the 

 luminary for oj^tical condensation of the radiant light, per unit of 

 focal area, as compared mth the luminary of our Fresnel four-wick 

 oil burner, has been in each case increased 109 per cent. With 

 reference to the jDcrfect combustion of these highly condensed flames 

 I may state that the efficiency for gas is exactly double that of the 

 London standard Argand burner, viz. when con;^uming gas of the 

 London standard of 16 candles, the light produced is at the rate 

 of 6 • 4, instead of 3 • 2, candles per cubic foot. In addition to a single 

 ring gas burner of this type we have two burners of ten rings of 

 flame, and models of their flames, one for gas and the other for mineral 

 oil. These burners are all of the Trinity House new pattern, both 



