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 Lesbieh. 



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, can 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. 



