418 Dr. Faraday on the Diamagnetlc conditions 



with or without the magnetic action, obtain any signs of heat 

 on the thermoscopic spiral above, even when the platinum 

 helix, not more than an inch below it, was nearly white hot. 

 This effect is, I think, greatly dependent upon the rapidity 

 with which hydrogen is heated and cooled in comparison with 

 other gases, and also upon the vicinity of the cold masses of 

 iron forming the magnetic poles, between which the hot gas 

 has to pass in its way upwards : and it is most probably con- 

 nected with the fact observed by Mr. Grove of the difficulty 

 of igniting a platinum wire in hydrogen. 



When the igniting helix was placed in coal-gas, it was 

 found that the hot gas was diamagnetic to that which was 

 cold; as in all the other cases. Here, again, an effect like 

 that which was observed in hydrogen occurred ; for when 

 there was no magnetic action, the ascending stream of hot 

 coal-gas could cause the thermoscopic spiral to revolve through 

 only 280° or 300°, in place of above 540° ; through which it 

 could pass when the surrounding gas was oxygen, air, or 

 carbonic acid ; and that even when the helix was at a higher 

 temperature in the coal-gas than in any of these gases. 



The proof is clear then that oxygen, carbonic acid, and 

 coal-gas, are more diamagnetic hot than cold. The same is 

 the case with air ; and as air consists of four-fifths nitrogen 

 and only one-fifth oxygen, and yet shows an effect of this 

 kind as strongly as oxygen, it is manifest that nitrogen also 

 has the same relation when hot and cold. 



Of the other gases also I have no doubt ; though to be quite 

 certain, they ought to be tried in atmospheres of their own 

 substance, or else in gases more diamagnetic at common tem- 

 peratures than they. The olefiant and coal-gases in air easily 

 bore the elevation of the helix to a full red heat, without in- 

 flaming when out of the exit-tube: the hydrogen required that 

 the helix should be at a lower temperature. Muriatic acid 

 and ammonia showed the division of the one stream into two, 

 very beautifully, on holding blue and red litmus paper above. 



There is another mode of observing the diamagnetic con- 

 dition of flame, and experimenting with the various gases, 

 which is sometimes useful, and should always be understood, 

 lest it inadvertently might lead to confusion. I have a pair of 

 terminal magnetic poles which are pierced in a horizontal 

 direction, that a ray of light may pass through them. The 

 opposed faces of these vertical poles are not, as in the former 

 case, the rounded ends of cones ; but, though rounded at the 

 edges, may be considered as flat over an extent of surface an 

 inch in diameter. The pierced passages are in the form of 

 cones, the truncation of which in this flat surface is rather 



