186 FRESNEL. 
to confine myself to the strict boundaries of truth, and 
the consciousness which I have of never having trans- 
gressed them, it should happen that this éloge should be 
accused of some exaggeration. Though I must avow it 
would be a reproach for which I should feel little as the 
friend of Fresnel, if it were incumbent on me to repel 
it, it would be solely in the capacity of the organ of the 
Academy : the office which I this day fill, in the name 
of my colleagues, ought to be marked by a precision 
and severity as great as that of the exact sciences with 
which it is concerned. 
REFRACTION. 
The labours of Fresnel almost exclusively relate to 
optics. In order to avoid tedious repetitions, I shall 
classify them, without regard to the order of dates, in 
such a way as to collect in a single group all those which 
relate to analogous subjects. The first which will engage 
my attention are the phenomena of refraction. 
A straight rod partly immersed in water appears bent 
or broken ; the rays by which we see the part immersed 
must, therefore, have changed their route or have been 
broken themselves, in passing out of the water into the 
air. It was till lately supposed that to this one observa- 
tion we were to restrict the entire knowledge of the an- 
cients on the subject of refraction. But in exhuming 
from the dust of libraries, where so many treasures are 
yet concealed, a manuscript of the optics of Ptolemy, it 
has been found that the School of Alexandria had not 
confined itself to establishing the mere fact of refraction ; 
for this work includes from all incidences, numerical de- 
terminations, tolerably exact, of the deviations of the 
rays, whether they pass out of air into water or into - 
