12 DR, FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXV.) 
its first place. The same efFeet recurred again and again. The amount of this change 
was very small, and there was reason to refer it to the pressure exercised by the 
magnet, when in action, upon the sides of the iron box ; for afterwards, when the box 
was placed in a vice and squeezed, the same motion in the fluid occurred ; and fur- 
ther, when the square blocks of soft iron (2733.) were kept apart by an under block 
of wood, so as not absolutely to touch and press the box, the effect was reduced to 
almost nothing, 
2735. Oxygen, nitrogen, carbonic acid and nitrous oxide gases, were then intro- 
duced successively into the iron box, and with exactly the same result as wuth 
air. No differenee appeared between oxygen and the other gases, greatly as they 
differ in magnetic and diamagnetic force and relations. Hydrogen and coal-gas were 
also subjected to experiment ; but when these gases were in the box there was a gra- 
dual recession of the indieating fluid, due, as I found, to the absorption of the gases, 
probably either by the varnish or cement or cork used at the gauge, or at the joints of 
the box. The delicacy of the gauge was thus made manifest ; but when the effect was 
taken into account, it was found that these gases were equally unaffected in bulk as 
the other gases by the magnetic influence. 
2736. The diameter of the gauge, at the place where the fluid was placed, was 
rather less than of inch. An amount of motion equal to of an inch 
was easily discerned. Comparing these numbers with the capacity of the gas-cham- 
ber, it would appear that if the gas in the latter had expanded or contracted to the 
extent of part, the result would have been visible ; or any difference approach- 
ing to this amount, between oxygen and nitrogen or the other gases, would have 
become sensible, hut no such effects or differences appeared. 
2737. As the establishment of either the occurrence or the absence of change of 
volume in gases, when under the magnetic influence, appeared to me to be of great 
and almost equal importance, I was led to consider whether, in the experiment just 
described, the circumstance of the gases having been subjected to the magnetic 
power in a field of equal force (2733.) might not have interfered with the production 
of the effect sought for; for such a field is that where the diamagnetic phenomena, of 
solid and liquid bodies, occur in the most unfavourable manner, and where indeed 
they almost entirely disappear. I therefore constructed another apparatus so that 
this condition was removed, and in which, if the particles of the diamagnetic gas, by 
any unknown disposition of the powers in action, tended only to pass from strong to 
weaker places of force, and being thus incapable of enlargement in the axial direc- 
tion, would only show that effect equatorialiy, the opportunity for their doing so 
should be present. 3^ 
2738. A cylinder of soft iron had the central parts removed in a 
lathe, until it had assumed the form of an hour-glass, or that repre- 
sented in fig. 3, which is to a scale of one-third. When placed be- 
tween the poles of the magnet instead of the former box, it was ex- 
