Heliacal Ring
   "This is a short helix, consisting of several layers of wire, with a large central opening. The ends of the wire are left free, to be inserted into the cups of the battery. [Below] are shown two semicircular pieces of soft iron, provided with handles for pulling. The handles are attached to the semicircles, by ball and socket joints, to prevent them from being twisted or wrenched by irregular pulling. When connection is made to the battery, and the  semicircles are passed within the coil,..., they adhere with very considerable force. 
   With thicker semicircles [above] the induced magnetism is sufficient to support a hundred weight or more, even with a small battery. ... If the flow of the current in the coil is stopped while they are applied to each other, they will still continue firmly attached; but once separated, will not adhere again.

   (from the 1851 Manual of Magnetism, pp 169-170)

Top: Middlebury College; Bottom: Harvard University

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