294 



Lord Elphinstone and C. W. Vincent. [Nov. 20, 



rested on one pole only, it was of course strongly held ; but on break- 

 ing contact it was at once set free, and fell off if not balanced ; the 

 magnetism of the |J core immediately falling to its minimum, as shown 

 by suspended test needles. If, however, the most minute point of 

 connexion existed between the armature and the other pole, in addi- 

 tion to its complete contact with the one it covered, it continued to 

 be firmly held long after battery contact was broken. 



It being thought that possibly the effects described were partly due 

 to molecular attraction of the iron atoms when brought into close 

 contact under magnetic stress, the poles were coated with a layer of 

 tallow, but if this was sufficiently thin, the magnet could still be 

 lifted by the armature after breaking battery contact. When the 

 tallow was broken into small lumps, allowing light to be seen be- 

 tween magnet and armature, the same result was obtained. 



Thus absolute metallic contact was found to be unnecessary for the 

 retention of a considerable amount of magnetism by the \J core and its 

 armature, when in magnetic circuit. With a piece of writing paper 

 interposed between the poles and armature, they were held together 

 with great force long after battery contact was broken ; but when the 

 distance was increased by the interposition of cards, nails, or wires, 

 to y-g of an inch, the residual attractive force was very much lessened. 

 When the magnetic circuit becomes more open the residual magnetism 

 dies away in about the same proportion as the attractive force of core 

 and armature, whilst under the influence of the battery current 

 it becomes less when the distance between them is increased. 



Interposition of thick glazed note paper caused such a diminution 

 of the residual magnetism that the magnet could no longer be lifted 

 by the armature. 



The experiment was varied by putting lengths of fine silk thread 

 straight across between the armature and the magnet ; in this, as in 

 the former experiments, the armature was firmly held, and the magnet 

 could be lifted by it. There was no point of actual metallic contact, 

 and light could be seen over both magnetic fields, except at the thin 

 lines where the silk threads were. The 581b. magnet, when lifted by 

 the armature, was thus literally suspended in the air (like Mahomet's 

 coffin) by the magnetism remaining in the almost closed circuit, and 

 this long after the exciting electric current had ceased. (The experi- 

 ments were made at intervals of four Lours, twenty-four hours, three 

 days, four days ; the armature had always ultimately to be wrenched 

 off.) 



The same result was obtained with plates or slips of zinc, copper, 

 platinum, silver, and aluminium foils, gutta-percha tissue, em- 

 broidery cotton, &c, and appeared to depend entirely on the distance 

 between poles and armature, irrespective of the nature of the inter- 

 posed body. 



