460 Institute of France. 
changes is distributed in an inverse ratio, and is exercised parti- 
eularly in the violet ray, and beyond this ray. 
M. Berard, a young chemist of Montpelier, who repeated with 
much precision both sets of experiments, ascertained their ex- 
aetiinite in several, respects: he even found that. the chemical 
power of light diminishes in proportion as we approach the 
middle of the spectrum, and that it vanishes beyond it. “But ac-~ 
cording to him, it is at the extremity of the red ray that the 
maximum of the heating power resides, and outside of the spec- 
trum it diminishes. M. Berard has also ascertained that these 
properties belong to the light reflected by ice, and to that which 
has been divided by the Iceland spar, as well as to the direct 
light. 
Decisive results have not yet been obtained on the power of | 
magnetizing iron, ascribed to the violet-coloured rays by M. Mo- 
richini, an ingenious Italian chemist. Although the magnetic 
needies exposed to these rays were apparently affected under 
certain circumstances, they exhibited no signs whatever in others, 
without our being able hitherto to account for this difference ; 
for, in both cases, all other causes known to produce polarity had 
been carefully enews: It is true that the summer of 1813 had 
not favoured this kind of inquiry, on account of the unsettled 
weather. 
Of all the phenomena which heat presents, the dilatation 
which it produces in bodies is that of which the laws admit of 
heing expressed most naturally by mathematical formule ; and 
the knowledge of these laws, which forms an essential part of 
‘physics, is also very important in a host of chemical experi- 
ments. M. Biot has been considerably occupied with this sub- 
ject ; and taking the dilatation of mercury as a term of compari- 
son, he finds that the real dilatation of other liquids may always 
be obtained by the sum of this dilatation, of its square, and of its 
cube ; multiplying each of these three terms by a particular co- 
efficient, which we must determine for every liquid, but which 
being once determined remains the same at all degrees. As the 
substance of the thermometer which contains the liquid under 
examination dilates also, the apparent dilatation is different 
from the true: nevertheless, M. Biot demonstrates that it takes 
place according to a similar law. He calculates afterwards, ac- 
cording to the experiments of M. De Luc, the coefficients adapt- 
ed for eight of the liquids whose laws it is most necessary to 
‘know; and shows that, these coefficients once obtained, its for- 
mula gives the dilatation of each degree equally well with the 
experiment. Lastly, he has made the application to the com- 
, bined dilatations of the vase and of the liquid, and has shown 
that 
