

Prof. Tyndall on the Polymagnet. 429 



between one pair of poles, and an ordinary diatnagnetic bar be- 

 tween the other pair, on sending the same current round both 

 magnets, the index of the former sets itself parallel to the polar 

 hue, while the index of the latter sets itself perpendicular to the 

 polar line, and thus the phenomena of magnetism and diamag- 

 netism address the eye simultaneously. 



6. In the same way, if a normal* magnetic bar be suspended 

 between one pair of poles, and an abnormal magnetic bar between 

 the other, the antithesis of their deportment may be made mani- 

 fest. The same antithesis is exhibited when we compare a nor- 

 mal diamagnetic bar with an abnormal one. 



7. And when between one pair of poles is suspended a normal 

 magnetic bar, and between the other pair an abnormal diamag- 

 netic one, the apparent identity of deportment of both bars is 

 rendered evident at once. The same identity is shown when 

 we compare the abnormal magnetic bar with the normal diamag- 

 netic one. 



8. Causing the points to face each other, instead of the flat 

 ends of the poles, and observing the directions given in the 

 paper spoken of, the curious phenomena of rotation on raising 

 or lowering the body from between the points, first observed 

 by M. Plucker, and explained in the paper referred to, may be 

 exhibited. 



9. To show that a bar of bismuth, suspended within a helix and 

 acted upon by magnets, presents phenomena exactly analogous 

 to those of soft iron, only always in opposite directions, let the flat 

 helix be replaced between the two electro-magnets. The bar of 

 bismuth used in experiments with the instrument now described 

 is 6 inches long and 0'4 of an inch in diameter. Suspended so 

 as to swing freely within the helix, its ends lie between the 

 moveable masses of iron which rest upon the electro-magnetic 

 cores. Four poles are thus brought simultaneously to bear upon 

 the bar of bismuth, and its action is thereby rendered both 

 prompt and energetic. The two poles to the right of the bar 

 must both be of the same name, and the two to the left of the 

 bar of the opposite quality. If those to the right be both north, 

 those to the left must be both south, and vice versa. On send- 

 ing a current from 10 or 15 cells round the helix, and exciting 

 the magnets by a battery of 4 or 5 cells, the current reversers 

 place the deflections of the bar entirely under the experimenter's 

 control. By changing the direction of the current in the helix 



* For the explanation of normal and abnormal bars see a memoir " On 

 the Nature of the Force by which Bodies are repelled from the Poles of a 

 Magnet," to be published in the forthcoming part of the Philosophical 

 Transactions. The paper will, iu due time, be transferred to the pages of 

 the Philosophical Magazine. 



