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LENSES FOR LIGHT-HOUSES. 271 
alent to that of 3,000 or 4,000 Argand 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 other, 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. 
