LENSES FOR LIGHT-HOUSES. 271 



alent to that of 3,000 or 4,000 Avgand lamps united ; 

 that is, eight times that produced by the beautiful sil- 

 vered parabolic reflectors of which our neighbours make 

 use ; it is also equivalent to the light which we should 

 obtain by uniting in one the third part of the total 

 quantity of the gas-lights which illuminate the streets, 

 the shops, and the theatres of Paris. Such a result does 

 not seem devoid of importance, if we remark that it is 

 obtained with a single lamp. In perceiving such power- 

 ful effects, the Government took care to authorize Fres- 

 nel to cause to be constructed one of his instruments, 

 and selected the lofty Tower of Cordouan, at the mouth 

 of the Gironde, as the point where it should be placed. 

 The new light-house was at length constructed in the 

 month of July, 1823. 



The light-house of Fresnel has since had for judges, 

 during seven consecutive years, the multitude of mari- 

 ners of all countries who frequent the Gulf of Gascony. 

 It was also studied assiduously at the place by skilful 

 engineers, who came expressly from the north of Scot- 

 land with a special mission from the British Govern- 

 ment. I shall here be the interpreter of the opinions 

 both of the one and the othei-, when I affirm that France, 

 since there the important invention of revolving lights 

 had its origin, possesses, thanks to the labours of our 

 scientific colleague, the most beautiful light-houses in the 

 world. It is always glorious to march at the head of the 

 sciences ; but we experience above all a lively satisfac- 

 tion in claiming the first rank for our country, when the 

 question relates to one of those happy applications in 

 which all nations are called upon to take an equal part, 

 and of which humanity will never have occasion to com- 

 plain. 



