on a magnetic needle- was rapidly succeeded by a series of minor 

 ones, all tending to establish the existence of an intimate connexion 

 between magnetism and electricity. The evidence, however, of that 

 connexion, resting, as it did, on the mutual influence of magnets 

 and wires in which electric currents passed, and in the development 

 or induction of magnetism by electricity, was positive on one side 

 only ; to render it conclusive, it remained to be shown that elec- 

 tricity could be excited by magnetism : and this, by a series of ex- 

 periments as simple as they are beautiful, founded on a train of 

 correct reasoning, Mr. Faraday has happily accomplished. 



Although the Council consider that the discovery of magneto-elec- 

 tricity fully entitles its author to the Copley Medal, they by no means 

 limit the value of the papers in which it is detailed to this discovery, 

 however important. Even the preliminary facts, as they fully esta- 

 blish volta-electric induction, had they at the time led no further, 

 would have been of the greatest value; but they were in hands in 

 which they could not long remain barren, and the expectation they 

 held out of important results was soon realized. Beyond the 

 details of the discovery, the author rapidly but clearly establishes 

 the laws according to which electric currents are excited bv a magnet. 

 He satisfactorily applies these laws to the explanation of a very in- 

 teresting class of phenomena previously observed, namely, the reci - 

 procal action of magnets and metals during rotation. He at the 

 same time establishes an important distinction among bodies which 

 had long been considered as associated by phenomena common to 

 them all ; and gives indisputable evidence of electric action due to 

 terrestrial magnetism alone. An important addition is thus made to 

 the facts which have long been accumulating for the solution of that 

 most interesting problem, the magnetism of the earth. 



The Council have awarded another Copley Medal to M. Poisson, 

 for his work entitled Nouvelle Theorie de V Action Capillaire. In this 

 work a great variety of problems are solved relative to molecular 

 attraction, some of which had not before been attempted ; but the most 

 remarkable feature of the work is, the conclusion which the author 

 draws, namely, that the elevation and depression of liquids in capil- 

 lary tubes are essentially dependent on the rapid variation of density 

 which takes place at the surface of the fluid, and without which, 

 according to the author, that surface would continue plane; this is at 

 variance with the theory given in the Mecanique Celeste, although 

 indeed Laplace notices this change of density at the surface, as a 

 necessary consequence of the action of the molecules upon each other 

 (Supp., x. livre, p. 74.) The theorems and expressions of M. Poisson 

 do not differ in form from those of the Mecanique Celeste ; but the con- 

 stants which are involved in these equations are not expressed by the 

 same definite integrals. No difference ensues in the consequences 

 which are deducible from them, because the law of molecular attrac- 

 tion being unknown, it is impossible to arrive at the value of these 

 constants a -priori, or otherwise than by observation. 



M. Poisson has calculated the vertical and horizontal pressures 

 upon a solid body plunged in a fluid : the value of the latter does not 



m 2 



