IN STUDYING QUESTIONS OF CHEMICAL MECHANICS. 395 
composition, will furnish a multitude of important experiments 
for explaining the molecular mechanism of chemical actions. If 
I am not deceived as to the tendency of these phenomena, they 
open a field of research among the most important as well as 
the most fruitful on which a chemist can enter. 
Lastly, the same processes have already been employed to 
follow the progress of the natural juices of vegetables in the 
various parts of their organs, taking as a guide the modifications 
undergone by the saccharine matters which these juices contain, 
in proportion as they are carried in the progress of vegetation 
from the roots into the trunk, from the trunk into the leaves, 
and as they redescend from these latter in the exterior canals 
near the surface, where the new ligneous layers are formed. I 
give here, in a note, the indication of several researches of this 
kind which have been already published ; but I present them less 
as finished investigations, than as essays, which deserve to be 
continued and still further extended*. 
77. I will mention, in conclusion, that, according to the ex- 
periments made by M. Melloni and myself, some years ago, the 
rotatory properties of rock-crystal are exerted also upon the calo- 
rific rays, and impart to them deviations of the same direction as 
to the luminous rays, that is to say, directed in the same way for 
each plate toward the right or left of the observer. By a neces- 
sary consequence of this property, when various plates of quartz, 
perpendicular to the axis of crystallization, are interposed si- 
multaneously, and in succession, in one and the same calorific 
beam previously polarized, their individual effects are added or 
compensated, according as the direction of their action is simi- 
lar or contrary. These experiments have been described in the 
Comptes Rendus de ? Académie des Sciences, t. ii. p. 194; but 
we have not ascertained whether the same property of modi- 
* Journal de T Institut: Sur quelques nouveaux faits pour servir 4 l'histoire 
de la végétation, tome i. p. 229. Déscription d’un appareil a double effet pour 
observer les mouvemens de la séve ascendante et la recueillir, tome ii. pp. 66 
and 222. Nouvelles Annales du Muséum d’ Histoire Naturelle: Sur le mouve- 
ment et la nature de la séve de printemps, tome ii. p. 271. Sur les variations 
lentes ou soudaines qui s’opérent dans les combinaisons organiques, tome ii. 
p- 335. Sur les transformations opérées par la vie végétale dans les produits 
carbonisés qui servent d’aliment aux jeunes individus, tome ii. p. 365. Sur 
Papplication de la polarisation circulaire a l’analyse de la végétation des grami- 
nées, tome iii. p. 47. [A translation of this memoir, together with the obser- 
vations of M. Chevreul on the same subject, will be found at p. 584 of the first 
volume of this work.] Comptes Rendus de l’ Académie des Sciences: Remarques 
et expériences de physique végétale,  l’occasion d’une Lettre cur la filtration 
des liquides a travers les tiges ligneuses, t. xii. p. 357. 
2Fr2 
