134 ANNUAL OF SCIENTIFIC DISCOVERY. 



on one side of the iron core, and the other on the other side, any dif- 

 ference in their tendency to set inwards or outwards from the axial 

 line causes them to take up their places of rest at different distances 

 from the magnetic axis ; and the power necessary to bring them to an 

 equidistant position becomes a measure of their relative magnetic or 

 diamagnetic force. 



In the first place, different gases were tried against each other, and 

 \vhen oxygen was one of them it went inwards, driving every other 

 outwards. The other gases, when compared together, gave nearly 

 equal results, and require a more delicate balance to determine the 

 amount of their respective forces. The author now conceived that he 

 had attained the long-sought power of examining gaseous bodies in 

 relation to the effects of heat and expansion separately, and proceeded 

 to investigate the latter point. For this purpose he prepared glass 

 bubbles containing a full atmosphere, or half an atmosphere, or any 

 other proportion of a given gas, having thus the power of diluting it 

 without the addition of any other body. The effect was most striking. 

 When nitrogen and oxygen bubbles were put into the balance, each 

 at one atmosphere, the oxygen drove the nitrogen out powerfully. 

 When the oxygen bubble was replaced by other bubbles containing 

 oxygen, the tendency inwards of the oxygen was less powerful : and 

 when what may be called an oxygen vacuum (being a bulb filled with 

 oxygen, exhausted, and then hermetically sealed) was put up, it simply 

 balanced the nitrogen bubble. Oxygen at half an atmosphere was 

 less magnetic than at one atmosphere, but more magnetic than other 

 oxygen at one third of an atmosphere, and that at one third surpassed 

 a vacuum. In fact, the bubble with its contents was more magnetic 

 in proportion to the oxygen it contained. On the other hand, nitrogen 

 showed no difference of this kind. Other gases (except olefiant and 

 cyanogen) seemed in this first rough apparatus to be in the same con- 

 dition. 



Hence the author decides upon the place for zero, and concludes 

 that simple space presents that case. When matter is added to space, 

 it carries its own property with it there, adding either magnetic or 

 diamagnetic force to' the space so occupied in proportion to the quan- 

 tity of matter employed ; and now, thinking that the point of zero is 

 well determined, he concludes to use the word magnetic as a general 

 term, and to distinguish the two classes of magnetic bodies into para- 

 magnetic and diamagnetic substances. Brewster's Philosophical 

 Magazine, Supplement. 



Owing to the importance of this subject, we insert a somewhat more 

 popular report of this lecture from the Mining Journal. 



After stating that he had shown, three years since, that oxygen is 

 highly magnetic, he said he had of late, by means of a peculiar dif- 

 ferential torsion balance, ascertained that as the oxygen is dense or 

 rare, it gains or loses for a given volume proportionally of its magnetic 

 power, and that as its temperature is lowered or raised, it also gains 

 or loses in the degree of its magnetic force. Nitrogen undergoes no 

 changes of this kind ; but the atmosphere, as a whole, is affected 

 through the oxygen it contains. These 1 changes are within the range 



