MEMOIR ON LIGHT. 135 
such a way as to turn always in the same direction. In 
1805, Malus was attached to the Army of the North. 
In 1806-7-8, he was sub-director of the fortifications 
of Strasbourg. In this capacity he presided over the 
reconstruction of the fortifications of Kehl, and made 
some very judicious remarks on the form of the revet- 
ments,* and applied an exact analysis to the determina- 
tion of their thickness. In 1809 he was recalled to 
Paris. He became major of engineers in 1810. The 
archives of the Committee of Arms prove that the in- 
spectors-general often consulted him with much advan- 
tage on the merit of works submitted to them. 
MEMOIR ON LIGHT.—COMPOSED IN EGYPT. 
We have henceforth to occupy ourselves only with 
the life of Malus as a physicist and member of the 
Academy ; without departure from this view, I may say 
a few words on the optical memoir which he composed 
in the hut at Lesbiéh. 
The author announces clearly, in the first part of the 
MS. memoir which I have before me, the object which 
he proposes ; this is to prove that light is not a simple 
substance ; that its constituent principles are caloric and 
oxygen, in a particular state of combination. To estab- 
lish this theory, he cites numerous facts furnished by 
chemistry, which prove that he was perfectly initiated, 
not only in the general principles, but even in the 
details of this science. It must be observed, however, 
that all the deductions of Malus, even the most plausible 
at the present day, ean be subverted by a single word ; 
it suffices to cite, in contradiction to all the phenomena 
* The masonry encasing and supporting the earthworks in a for- 
tification. 
