MAGNETIC CHARACTER OF OXYGEN GAS. 
23 
diminish its diamagnetic character, until, when reduced to the condition of a vacuum, 
it should disappear. In other words, if two opposed portions of tne same magnetic 
gas, one rarer than the other, were subjected at once to the magnetic foice, the 
denser ought to approach the axial line, or be drawn into the place of most intense 
action ; whereas if two similarly opposed portions of a diamagnetic gas were subjected 
to the magnetic action, the more expanded or rarer gas ought to go inwards to the 
place of strongest action. 
2/80. Several bulbs of oxygen (fig. 8), similar in arrangement to those g 
already described (2772-), and very nearly alike in size, were prepared 
and hermetically sealed, after that the quantity of gas within them had 
been reduced to a certain degree by the air-pump. The first contained 
the gas at the pressure of one atmosphere ; the second had the gas at half 
an atmosphere, or 15 inches of mercury; the third contained gas at the 
pressure of 10 inches of mercury; and the fourth, after being filled with 
oxygen, was reduced to as good a vacuum as an excellent air-pump could 
effect. When the first of these was compared with the other three, the 
effect was most striking ; opposed to the half atmosphere, it went towards 
the axis, driving the expanded portion away; when in relation to the one- 
third atmosphere, it went inwards or axially Muth still more power; and 
when opposed to the oxygen vacuum, it took its place as close to the iron 
core as in the former case, when contrasted with nitrogen (2774.) ; and it was ma- 
nifest that the diamagnetic power of the glass tube which inclosed it (2775.), was 
the only thing which prevented the oxygen from pressing against the iron core occu- 
pying the centre of the magnetic field. 
2781. On experimenting with the other tubes exactly the same result was obtained. 
Thus the tube with one-third of an atmosphere, in association with the vacuum tube, 
went inwards, driving the other outwards, i. e. it was more magnetic than the vacuum ; 
but in association with the one-half atmosphere tube it went outwards, whilst the 
denser gas passed inwards. Any one of the tubes, if associated with another having 
a rarer atmosphere, passed inwards or magnetically, whilst if associated with others 
having denser atmospheres it passed outwards, being driven off by the superior mag- 
netic force of the denser gas. As far as I could ascertain in these preliminary forms 
of experiment, the tendency inwards or axially appeared to be in proportion to the 
density of the gas; but the exact measurement of these forces will be given hereafter. 
2782. Thus oxygen appears to be a very magnetic substance, for it passes axially, 
or from weaker to stronger places of force, with considerable power; a conclusion in 
accordance with the result of former observations*. Moreover it passes more power- 
fully when dense than when rare, its tendency inwards being apparently in propor- 
tion to its density. Hence, as the oxygen is removed, the magnetic force disappears 
with it, until when a vacuum is obtained, little or no trace of attraction or inward 
force remains. No doubt it may be said that dense oxygen is less diamagnetic than 
* Philosophical Magazine, 1847, vol. xxxi. pp. 410, 415. 
