330 Prof. Vaucher on the Fall of Leaves. 



In setting out from this theory, M. Poisson announces that 

 his memoir contains general formulae which give at once the 

 action produced in a state of rest and in a state of motion. 

 The first embrace the magnetic phenomena long known ; and 

 the author thinks that the second are sufficient to explain the 

 phenomena discovered by M. Arago. 



It follows from M. Poisson's calculations, that there is no 

 dependence between the two sorts of actions, and that experi- 

 ment alone is capable of determining the respective co-efficients 

 of the values of these actions. 



Art. XXVI. — On the Fall of Leaves. By Professor Vaucher 



of Geneva. * 



Among the phenomena of Nature obvious to every eye, and 

 interesting in many respects, is the Fall of the Leaf — that 

 period of the season when the foliage of summer, having per- 

 formed its office, shrivels and falls off, to make way for the 

 buds and leaves of a future summer. This phenomenon has 

 afforded to the Moralist and the Poet many of their most beau- 

 tiful allusions, and has served for an illustration of that alternate 

 decay and renovation which seem to pervade all the classes 

 of organized matter. To the medical philosopher the Jail of 

 the leaf is no less interesting, as having some how or other a 

 connection with certain states of health and disease ; and com- 

 mon observation has long regarded this epoch as peculiarly 

 marked in our variable climate by a more than usual morta- 

 lity — when the fairest hopes of many families " drop off like 

 leaves in autumn." The structure and functions of leaves — 

 their use to the plants of which they form a part — and their 

 use in the general economy of nature — have long occupied 

 the attention of the vegetable physiologist ; but the causes of 

 defoliation, and the means by which that defoliation is accom- 

 plished have been less successfully investigated. In a paper 

 by Dr Fleming in the seventh Number of this Journal, that 

 able naturalist has made some judicious remarks upon the de- 

 foliation of trees, and upon the classification of systematic 



• Mem. de la Soc. de Physique et d'Hitt. A T at- de Geneve, vol. i. p. 120- 



