UPON GASES AND LIQUIDS. 55/ 



7. I placed the two halves of the keeper B (see paragraph 2.), 

 with the conical apices screwed into them, upon the surfaces of 

 the poles, in such a manner that the distance of the two apices 

 from each other amounted to 3*5 millims. Beneath them I 

 placed a previously-heated thick plate of platinum, and covered 

 the whole with the open case of the torsion- balance mentioned 

 above. Small pieces of iodine were placed upon the plate of 

 platinum, and as soon as a very narrow column of vapour of 

 iodine ascended perpendicularly between the apices of the poles 

 the magnetism was excited by closing the circuit. The column 

 which was previously ascending perpendicularly, immediately 

 expanded above the apices of the poles, so as to form a para- 

 bola in the equatorial plane ; this, especially on the concave side, 

 where the violet colour Avas most intense, was very accurately 

 defined, and remained perfectly distinct for an elevation of 100 

 to 150 millims. We shall hereafter allude to a similar figure 

 formed by the soot of a tm-pentine flame ; and as a sketch of this 

 appearance is subjoined, further notice of it will be omitted at 

 present. 



The experiment described in the above paragraph shows be- 

 yond a doubt that the vapour of iodine is repelled by both the 

 poles of a magnet. 



8. This result is confirmed when the two parallelopipedal 

 halves of the keeper (A.) are applied by their broad surfaces. If 

 the ascending vapour of the iodine is then conducted between 

 the two surfaces of the poles of the halves of the keeper, it be- 

 comes displaced laterally (in an equatorial direction) ; and if it 

 be allowed to ascend by their side, it is repelled outwards. This 

 effect is found to be most intense when the magnetic tension is 

 increased by again approximating the two keepers to within 

 3 millims. to 4 millims. 



9. In interpreting the result obtained in the two preceding 

 paragraphs, we must not forget that the iodine vapour is sur- 

 rounded by air. This iodine vapour, in proportion to the repul- 

 sion which it experiences by the poles of the magnet, either be- 

 comes diamagnetic, and if so, more powerfully diamagnetic than 

 the air, if the latter is at all so, or it exerts a neutral re-action. 

 But for the air to become magnetic, the former, if not diamag- 

 netic, must still be less magnetic than the latter*. The former 



• Tlie remarkable experiment of Farada}', in which he suspended a glass 

 tube filled with a solution of protosuiphate of iron in a similar solution between 



