576 PLUCKER ON THE ACTION OF THE MAGNET 



the cuiTent of six elements was transmitted through it, the 

 spiral became white hot, a heated current of air quietly ascended 

 between the apices of the poles under the case of the torsion- 

 balance, and threw a well-defined shadow upon a sheet of white 

 paper which was held behind it. Unfortunately the sun com- 

 pletely disappeared just at the moment when the magnetism was 

 about to be excited by closing the circuit. But as Faraday has 

 made the corresponding experiment by shoAving the equatorial 

 deflection of an ascending current of heated air, by thermometers 

 placed above and at the sides, there is no longer any doubt that 

 even in my arrangement the shadow which directly ascended 

 would have separated into two parabolic branches. 



56. Every one, who has but once seen the smoke from a 

 flame of turpentine or the vapour of iodine ascending between 

 the apices of the poles, must also be convinced how by Faraday's 

 beautiful process, — in which he placed vessels above (or beneath), 

 and on the side of the gaseous current whilst directly ascending, 

 to receive it, and subsequently found that those gases, which are 

 more diamagnetic than the air, did not enter the upper (or under) 

 vessel, but that placed at the side, — we may obtain general re- 

 sults. But when the examination of the vai-ious gases becomes the 

 question, my series of experiments, in which I confined myself 

 to the action of the magnet upon visible gases, — the experiment 

 of causing colourless gases to ascend in coloured gases, and thus 

 rendering them visible, was neither carried out by myself nor 

 was its practicability at all tested, — become inferior to those 

 of Faraday. 



57. However I shall finally again direct attention to the expe- 

 riment described In the earlier paragraphs, viz. that of directly 

 proving the diamagnetism of the air by its rarefaction in exactly 

 the same manner, as its eayjansion by heat is shoivn by an ordi- 

 nary air-thermometer. Although I was then compelled to report 

 the failure of the experiment, which was twice performed in an 

 unsatisfactory manner, still I never lost sight of it, nor doubted 

 for an instant of its ultimate success. I am now able to assert that 

 it has succeeded most beautifully. 



I appUed the two halves of the keeper (C), with their semi- 

 circular ends turned towards each other and fixed at the very 

 short distance of 5 mlUlms. apart, upon the poles of the horse- 

 shoe electro-magnet ; and had a vessel made of thin sheet brass, 

 which fitted as accurately as possible between the two keepers, but 



