2 NOTICES OF THE MEETINGS [Jan. 24, 
A double cone of iron (the apices of the cones meeting in a point, 
and the cones being equal and similar,) was fabricated of such a 
length as to complete the magnetic circuit when placed between the 
poles of the large electro-magnet i in possession of the Royal Institu- 
tion. Mr. Faraday directed attention to this hourglass-shaped 
piece, and showed how, by such an arrangement, extreme power is 
exerted at the place without any chance of ‘change in the form of the 
parts. Very small soap-bubbles were blown by means of a glass 
tube drawn to a fine point, from a bladder filled with oxygen. It 
was observed that these bladders so filled were drawn forcibly in- 
wards to the apices of the cones, but that no such effect followed 
when bubbles were filled with nitrogen. Another experiment, 
which was visible all over the room, at once demonstrated the 
same fact, and illustrated a differential mode of measuring the 
magnetic force of oxygen. A delicately balanced wire was sus- 
pended from its centre of gravity by 10 fibres of the cocoon of the 
silk-worm; from the extremities of a small cross bar at one end of 
this wire were hung small glass bubbles ; and the whole was so ad- 
justed that the bubbles were on opposite sides of the apices first 
described, each hanging near to it but not in contact with the 
iron, and each equidistant from it. Therefore any difference of 
magnetic influence on the bubbles or their contents would be indi- 
cated by the bubble so affected being drawn inwards. In order 
to render such motion widely visible, the other arm of the balance 
just described was converted into a long indicating lever, con- 
structed of a straw for the sake of lightness. To the extremity of 
the longer end a slip of silk was attached to catch the eye, and the 
lever was shielded from the currents in the room by being placed 
within a glass balloon two feet in diameter. By the motion of the 
lever it was seen, when one of the bubbles was filled completely or 
partially with oxygen and the other with nitrogen, that nitrogen, 
whether dense or rare, was totally unaffected by the magnet, and 
that oxygen was magnetic in direct proportion to its density in the 
bubble ; and that the force required to set the bubble of oxygen 
(one atmosphere) in motion towards the magnet was one-tenth of a 
grain for one-third of a cubic inch of oxygen. 
Certain peculiarities in the exertion of the power which is here in 
action, not as a central, but as an axial force, were then referred to. 
The inference from the experiment, supported by other experi- 
ments on bubbles containing air, is — that as oxygen enters into the 
atmosphere in a constant proportion, and as the magnetic power 
of oxygen varies directly with its density, definite variation must 
take place in the magnetic power of the atmosphere in different 
states. 
Mr. Faraday was led to inquire whether any separation of oxygen 
from nitrogen in a mixture of these gases could take place, as happens 
when a magnet is presented to a mixture of iron filings and sand. 
To test this idea he applied to the conical angle (so often de- 
