386 Roijul Academy of Sciences of Paris. 



menl of Calvados, proposes to publish a general work upon 

 Lichens. He announces that he has already in his possession 

 more than 1000 species named and classed. 



INI. de Montferrand read a Memoir on Electro-dynamic 

 Phaenomena. The principal aim of this memoir is to show 

 that all the experiments made upon an indefinite vertical con- 

 ductor, submitted to the action of a horizontal magnet, are 

 mathematical consequences of the theory by which M. Ampere 

 explains the properties of magnets, and of the formula which 

 he has given to represent the mutual action of two infinitely 

 small portions of electric currents situated in any position what- 

 ever in space : in order to prove this, the author has calculated 

 successively, according to this formula, the action of an inde- 

 finite rectilineal conductor upon a small rectilineal current, 

 upon a circle situated in a plane parallel to the conductor, 

 and upon several systems of circles subjected to the same con- 

 ditions : he has obtained the following results : 



1°. The action of a rectilineal current indefinite both ways, 

 upon a small current situated in any position whatever in space, 

 is perpendicular to that small current. 



2°. When a current which follows any plane curve is sub- 

 jected to the action of a current indefinite both ways, and re- 

 volves round an axis perpendicular to the plane of the curve, 

 and to the indefinite current ; the sum of the momentums of 

 the forces v.hich tend to make the conductor revolve, is tlie 

 same in all positions. 



3'^. The mutual action of an indefinite current, and of a 

 small current situated in any manner in space decomposed in a 

 hue perpendicular to the indefinite conductor, is in the direct 

 ratio of the cosine of the two directions, and in the inverse 

 ratio of the simple distance. 



4°. When a Voltaic current follows a curve symmetrical 

 with relation to an axis, this curve has no action in the direc- 

 tion of the indefinite current upon an indefinite current parallel 

 to its plane and perpendicular to the axis. The circle possesses 

 this property, from being symmetrical with relation to all Its 

 diameters. 



5°. The action of a small circular current upon an indefi- 

 nite conductor, parallel to its plane, is proportional to the sur- 

 face cf the circle, and in an inverse ratio of the square of the 

 distar.ce; it is independent, as to its intensity, of the relative 

 positions of the circle, and of the conductor. 



6°. The angle formed by the direction of the force with 

 the plane of the circle is always double the angle formed with 

 the same plane, by a perpendicular falling from the centime of 

 the circle upon the indefinite current. 



7°. The 



