DIFFERENTIAL MAGNETIC ACTION OF GASES. 
19 
Fig. 5. 
side of the tube, fig. 5. The dependent position supplies, 
in inclosed spaces or atmospheres, an exceedingly delicate 
indicator ; and even when the bubble is on the side of the 
tube it still forms a very valuable instrument, for it freely 
moves round the tube as axis ; and as it possesses a 
certain degree of steadiness, it can be held in the mag- ^ 
netic field in any position, and by its motion to or from 
the axial line, shows very well the magnetic or diamag- 
netic condition of the gas contained in it in relation to 
the surrounding air. 
2763. If the mouth of the tube be turned upwards, bubbles of the thinnest texture 
can be blown ; but they are then also very unstable in position, and run to the side of 
the tube ; they can be used as indicators, as above (2762.). If the mouth of the tube 
be made broader, the bubbles, being thin, can be retained standing on the extremity ; 
but as their attachment is larger, so they require more force to move them sideways, 
and they lose in delicacy of indication. 
2764. It is convenient, in working with such bubbles, to make them nearly equal in 
size and thickness for the same set of comparative experiments. I usually employ them 
about half an inch in diameter. On blowing such a bubble with air, in the dependent 
position, placing it in the angle of the double pole on a level with the axial line (fig. 6), 
and then putting on the magnetic power, by the use of twenty pair of Fig. 6. 
plates the bubble was deflected outwards from the axial line (or 
equatorially) with a certain amount of force, and returned to its first 
position on the interruption of the electric current. The deflection 
was not great, and being due to the water of the bubble, gave an indication of the 
amount of that effect, to be used as a correction in experiments with other gases. 
2765. Nitrogen in air. — A bubble of nitrogen went outwards or equatorially in 
common air with a force much surpassing the outward tendency of a bubble of air 
(2764.), in a very striking and illustrative manner. It was often driven up from the 
end to the side of the tube ; and when on the side, if presented inwards, it was driven 
to the outside of the tube, and however the tube was turned round, kept that position 
as long as the magnetic force was maintained. This effect is the more striking when 
it is considered that four-fifths of the air itself is nitrogen gas. 
2766. Oxygen in air. — The effect was very impressive, the bubble being pulled in- 
wards or towards the axial line sharply and suddenly, exactly as if the oxygen were 
highly magnetic. The result was expected, being in accordance with the phenomena 
presented by oxygen and nitrogen in a former investigation of the diamagnetic phe- 
nomena of the gases 
2767. Nitrous oxide and ol^ant gases in air. — Tlie bubbles went outwards or dia- 
magnetically with a force much greater than that due to the effect of the water of the 
bubble, proving the relation of these gases to air, and according with the results 
formerly obtained with streams of these substances-j'. 
* Philosophical Magazine, 1847, vol. xxxi. pp. 410,415. 
. D 2 
t Ibid. p. 411. 
