[67] Davy observes, that there are many facts recorded in the Philosophical Transactions, which prove the magnetising powers of lightning: one in particular, where a stroke of lightning passing through a box of knives, rendered most of them powerful magnets.--_Philosophical Transactions_, No. 157, p. 520, and No. 437, p. 57. In the progress of electrical discoveries, the similarity between electricity and magnetism had not escaped observation,[68] and some philosophers had even attempted to establish the existence of an identity or intimate relation between these two forces. The experiments of Ritter, however, alone appeared to offer any confirmation of the supposed analogy; but so obscure was his language, and so wild and hypothetical his views, that few, if any, of them were repeated either in France or England, and their results were for a long time wholly disregarded. [68] The phenomena of many crystallized minerals which become electric by heat, and develope opposite electric poles at their two extremities, offered an analogy so striking to the polarity of the magnet, that it seemed hardly possible to doubt a closer connection of the two powers. The developement of a similar polarity in the Voltaic pile pointed strongly to the same conclusion; and experiments had even been made with a view to ascertain whether a pile in a state of excitement might not manifest a disposition to place itself in the magnetic meridian.--_Herschel's Discourse_, p. 340. In a work, entitled "Recherches sur l'identité des Forces Chimiques et Electriques," published by M. Oersted in the year 1807, the subject was resumed, and the author advanced the hypothesis,[69] which twelve years afterwards conducted him to one of the most important discoveries of the present age, and which has given origin to a new science, termed ELECTRO-MAGNETISM.[70] [69] The hypothesis was this:--"In galvanism, the force is more _latent_ than in electricity, and still more so in magnetism than in galvanism; it is therefore necessary to try whether electricity, in its _latent_ state, will not affect the needle." This passage may be thus explained: When the Voltaic circuit is interrupted, it possesses opposite electrical poles; and when continuous, it no longer affects the electrometer, or the electricity becomes _latent_, which is the condition theoretically required for the manifestation of its magnetic action: and the fundamental experiment of Oersted proved that, under these circumstances, the compass needle was affected. [70] Mr. Herschel, in speaking of the pertinacity with which Oersted adhered to the idea of a necessary connection between electricity and magnetism, observes, that there is something in it which reminds us of the obstinate adherence of Columbus to his notion of the necessary existence of the New World.