were discovered by Sturgeon in 1825. Of two Magnets made by a process
devised by M. Elias, and manufactured by M. Logemeur at Haerlem, one,
a single horse-shoe magnet weighing about 1 lb., lifts 28½ lbs.; the
other, a triple horse-shoe magnet of about 10 lbs. weight, is capable
of lifting about 150 lbs. Similar magnets are made by the same person
capable of supporting 5 cwt. In the process of making them, a helix of
copper and a galvanic battery are used. The smaller magnet has twice
the power expressed by Haecker’s formula for the best artificial steel
magnet.
Subsequently Henry and Ten Eyk, in America, constructed some
electro-magnets on a large scale. One horse-shoe magnet made by them,
weighing 60 lbs., would support more than 2000 lbs.
In September 1858, there were constructed for the Atlantic-telegraph
cable at Valentia two permanent magnets, from which the electric
induction is obtained: each is composed of 30 horse-shoe magnets, 2½
feet long and from 4 to 5 inches broad; the induction coils attached to
these each contain six miles of wire, and a shock from them, if passed
through the human body, would be sufficient to destroy life.