Note 2 — THE ELECTRO MAGNETIC TELEGRAPH.

The term magnet, here, is synonymously used with the iron for the magnet, as the simple iron is not a magnet, except when subjected to the action of the battery through the helices of wire around it. It would confuse the reader, if this distinction be not kept in view. Permanent magnets are those which retain their magnetism when once they are charged. They are always made of steel, and usually bent in the form of a horse-shoe. Sometimes they are of a single plate of that form, and others are constructed with many plates, side by side, fastened together so as to present a compact magnet of the same form. They are distinguished from Electro Magnets from the fact, that the soft iron of the latter depends upon the influence of the galvanic fluid for its magnetism, and retains it only so long as the soft iron is under its influence, while the former, when once submitted to the influence of the galvanic fluid, retain their magnetism permanently.