188 MALUS. 
an. TX., 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 
Buccessively 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 :— 
