138 MALUS. 



an. IX., that Malus was occupied theoretically with that 

 most important meteorological question, the distribution 

 of heat in different climates. I have never been able to 

 find what has become of this work. 



TREATISE ON ANALYTICAL OPTICS. 



On the 20th April, 1807, Malus presented to the first 

 class of the Institute, a treatise on analytical optics, in 

 which he treats of rays of light by geometry of three 

 dimensions. 



The choice of academicians to whose examination the 

 work was entrusted, sufficiently indicates the reputation 

 which the author had already acquired. These commis- 

 sioners were Lagrange, Laplace, Monge, and Lacroix. 

 The report of this distinguished commission was pre- 

 sented by Lacroix, and bears date the 19th October, 

 1807. 



The author of the memoir examines the nature and 

 relative position of the surfaces formed by straight lines 

 successively intersecting one another according to given 

 laws. After having deduced from his researches some 

 general theorems, of a very remarkable kind, he pro- 

 ceeds to make an application of them to the case of rays 

 of light proceeding in similar directions, either by reflex- 

 ion or by refraction. He thus generalizes the theory 

 of plane caustics, formerly broached by Tschirnhausen. 

 Among the curious results which he deduces from his 

 formulas, we will merely quote the following : 



" Reflexion and refraction furnish sometimes optical 

 images which are erect in one of their dimensions and 

 inverted in the other." 



The report, for which I will not presume to substitute 

 my personal opinion, concludes in these terms : 



