454 SEC. 12. APPLIED MECHANICS. 



finished at the beginning of 1827, but they could not be tried until after the 

 inventor's death. 



This study shows how Fresnel came to invent not only the section of cata- 

 dioptric rings, and the use of these rings hi fixed light apparatus, but also 

 their applying to annular lenses for flashing lights or for fixed lights. By 

 uniting the pieces of dioptric elements and of catadioptric rings manufactured 

 in Fresnel' s time for the apparatus of the St. Martin's Canal, the annular lens 

 exhibited under No. 6 was formed, and it may be considered as the type 

 of all the annular lenses used in the lighthouses of different order. 



The model in wood, No. 7, represents an apparatus similar to the preceding, 

 but having a diameter of 0'25 m instead of 0'20 m . It is a study of Fresnel's 

 which he did not carry out. 



Lamp Burners. 



No. 8. One of the first burners, with four concentric wicks, constructed 

 after experiments made by Arago and Fresnel in 1819-20. 



No. 9. Burner, with two wicks and outer wrapper for directing the draught, 

 constructed by Henry Lepaute in 1845. 



No. 10. Burner, with five wicks, of graduated shape, for mineral oil, with 

 the last improvements adopted in the lighthouses of France, 1876. 



When Fresnel undertook the improvement of lighthouses, he had to solve 

 not only the problem of construction of the lenses, but also that of lamps with 

 several wicks. The chemist Guyton-Morvau had already studied the ques- 

 tion. In a paper read by him at the Institute in 1797, he stated that he had 

 constructed, 10 years before, a lamp on the argand principle, with three 

 concentric circular wicks, each having an inner and an outer draught. 

 He acquired great intenseness, but the solderings of the burner were de- 

 stroyed by the heat. About 1800, the watchmaker Carcel invented the lamp 

 that bears his name, and in which the oil at the bottom is forced up by a 

 pump towards the burner above which it overflows. This invention was to 

 lead towards solving the problem of lamps with many wicks. Consequently, 

 when Arago and Fresnel began, in 1819, their experiments with lamps, they 

 forced up the burner oil in superabundance so as to refresh it, and thus avoid 

 the inconvenience met with by Guyton-Morvau. The first trial took place 

 in September 1819 with two-wicked and three-wicked burners, constructed 

 after Fresnel's designs. After several hesitations, respecting chiefly the 

 width to be adopted for the draught between the wicks, they succeeded in 

 constructing a four-wicked burner that gave good results. It was tried 12th 

 May 1820, in presence of the Lighthouse Committee. The burner exhibited 

 under No. 8 is one of those that were constructed according to this first 

 type. 



The two-wick burner, No. 9, was constructed by Henry Lepaute in 1845, 

 for the lighthouse of Schevening in Holland. It has an outer cylinder for 

 dividing the draught generated between the glass and the burner, and 

 throwing back a part of it upon the light. It is the first application of this 

 cylinder which exists in all modern burners. 



The five- wick burner, No. 10, is a model of those now constructed for 

 using mineral oil in the French lighthouses. It contains an appendage 

 through which the oil must pass before reaching the upper part of the 

 burner. This said piece, of which the arrangements were invented by 

 M. Denechaux, acting engineer in ordinary at the lighthouse depot, is 

 intended to secure a continuous level, and comprises three tubes, juxtaposed, 

 and open on the upper part at the proper height ; the central tube springs 

 from the small reservoir which forms the basis of the burner, and in which 

 the oil is forced by the machinery of the lamp ; this oil, having no other exit, 

 rises in the tube, and, arriving at the [top, flows into the second tube, which 



