far tlie purposes of Illumination in Lighthouses. 41 



VENSON, the Engineer to the Scottish Lighthouse Board, on the 

 subject of introducing the lenses into the Northern Lighthouses. 

 The origin and history of this communication is as follows. 



Between the years 1818 and 1820, some experiments had 

 been made in France, with the view of fitting up lighthouses with 

 Lenses, a method which had been in use in England in the 

 Lower Lighthouse of the Island of Portland since 1789 *. The 

 French had proposed to use Lenses in connection with a very 

 powerful lamp, the particulars of which were communicated in 

 a letter from Major COLBY to Mr STEVENSON. On the receipt 

 of this letter, Mr STEVENSON stated to me his intention of inves- 

 tigating the subject, in reference to the use of lenses in light- 

 houses. I immediately pointed out to him the improvements in 

 the construction of lenses, and the method of arranging them 

 for the purposes of illumination, which I had suggested in the 

 Edinburgh Encyclopedia ; and he proposed that we should make 

 some experiments, with the view of introducing them into the 

 Northern Lighthouses. Before proceeding, however, to this in- 

 quiry, Mr STEVENSON was anxious to obtain an account of what 

 had been done in France ; and having afterwards understood 

 that the Cordouan Lighthouse on the French coast was to be 

 fitted up with lenses, he stated it to be his intention to make per- 

 sonal observations upon it, whenever the alteration on that light- 

 house should be completed. 



Unfortunately, however, the years 1820, 1821 and 1822 pass- 

 ed away, without any thing being done to ascertain the merit 

 of my invention for lighthouse illumination. In the beginning of 

 November 1 822, Mr STEVENSON and I received copies of a memoir 

 by M. FRESNEL, entitled, Memoir e sur un Nouveaux Systeme d'Eclai- 

 rage des Phares. This memoir was read at the Academy of 



* The lenses in this lighthouse, which are two in number, are twenty-two inches 

 in diameter. 



VOL. XI. PART 1. F 



