Fig. 25
Ampère's Molecular Currents
Though propounded more than eighty years ago, this theory is still in harmony with all facts and phenomena in the domain of magnetism known to-day. It is important to remember, when thinking of this physical theory, that the Amperian currents in question are confined to the molecule, and that they do not flow from one molecule to another. Critics have urged against the theory that the molecules must be heated by the circulation of these elementary currents, to which objection it has been replied that, as we know nothing of the nature of the molecule, we cannot say that it offers any resistance to the current; and, therefore, we cannot affirm that there is any development of heat due to the circulation of these elementary currents.
It is to Ampère's credit that he was also the first to propose a practical application of Oersted's discovery, an application that was nothing less than the electric telegraph itself. He suggested that the deflection of the magnetic needle could be used for the transmission of signals from one place to another by means of as many needles and circuits as there are letters in the alphabet. If Ampère had only recalled the optical and mechanical telegraphs in use in his day, such as the swinging of lanterns by night and wigwagging of flags and the movements of semaphores by day, he might have reduced his twenty-four circuits to one, using the two elements, viz., motion of the needle to the right and motion to the left, to make up the entire alphabet. Morse substituted the dot and the dash for these deflections, and thus rendered the reception of messages automatic and permanent.
In connection with this proposal to use a magnetic needle for the transmission of intelligence, the reader will no doubt recall the lover's telegraph, so beautifully described by Addison in the "Spectator" for December 6th, 1711; but ingeniously conceived as it was, this magnetic telegraph was purely and simply a creation of the imagination.
This canny conceit has been attributed to Cardinal Bembo, the elegant scholar and private secretary to Pope Leo X.; but it was his friend Porta, the versatile philosopher, who made it widely known by the vivid description which he gave of it in his celebrated work on "Natural Magic," published at Naples in 1558.
This sympathetic telegraph consisted, we are told, of a magnetic needle poised in the center of a dial-plate, with the letters of the alphabet written around it. The two fortunate individuals privileged to hold wireless correspondence with each other having agreed as to the day and the hour, proceed to the room in which the wonderful instrument is kept, where, as soon as one of them turns the needle of his transmitter to a letter, the distant needle turns at once in sympathy to the same letter on its dial!
Such is the power of magnetic sympathy, that the instruments will work successfully though hills, forests, lakes or mountains intervene! Porta has it: "To a friend at a distance shut up in prison, we may relate our minds; which, I do not doubt, may be done by means of compasses having the alphabet written around them."
