524 Prof. De la Rive on the Action of Magnetism upon 



becomes completely covered, when it is negative, with a beautiful 

 violet sheath, which contracts under the influence of the magnet. 

 The top of the iron rod, which is then positive, is surrounded by 

 a beautiful halo of a somewhat rosy- white colour, 3 centims. 

 broad, and very distinctly stratified. Magnetization causes 

 marked contraction in the halo, and causes the striae to approach 

 closer together without diminishing their number; it further 

 causes it to rise up, giving to it the shape of a pear resting with 

 its base upon the magnetic pole. When this pole is the nega- 

 tive electrode, a magnificent violet- coloured tuft, as we have 

 already seen, issues from it, and becomes erect when the mag- 

 net is in action. 



All the phenomena that we have here described prove in a 

 striking manner the molecular differences presented by the 

 various elastic fluids, even when greatly rarefied. Thus in the 

 case of hydrogen, although this gas is a very good conductor of 

 electricity, the electric jets obey with difficulty, and only to a 

 slight extent, the action of the magnet, probably on account of 

 the low density of the gas. With air and nitrogen the state of 

 things is just the opposite, especially when these gases are moist. 

 The singular property possessed by the electric jet of dividing 

 into several distinct jets, instead of spreading out, under the in- 

 fluence of magnetization, when the medium which it traverses 

 contains a greater or less quantity of vapour, would seem to in- 

 dicate on the part of the vapour greater cohesion than is pos- 

 sessed by the gases properly so called, if it be allowable to talk 

 of cohesion in relation to such highly rarefied elastic fluids. It 

 is also possible that this division into jets is nothing more than 

 the result of an optical illusion due to a very rapid succession of 

 jets starting from different points, but not simultaneous. This 

 is a point for further examination. 



However this may be, it is evident that the study of the stra- 

 tification of the electric light, and of the action of magnetism on 

 the discharge in different gaseous media, reveals differences 

 among these media which can only be due to differences of mole- 

 cular constitution. Density, in particular, would seem to exert 

 a great influence upon phenomena of this kind, since we find 

 them exhibited to such a small extent by hydrogen, whereas 

 aqueous vapour, and especially the vapours of alcohol and ether, 

 exhibit them in such a marked manner. The special nature of 

 the particular elastic fluids in reference to the greater or less 

 resistance they oppose to the transmission of electricity must 

 doubtless also come into play. It is therefore not impossible 

 that a more detailed and searching examination of the pheno- 

 mena we have been considering, and in particular of those con- 

 nected with the action of the magnet on electric currents pro- 



