14 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXV.) 
with it, or nearly so, so that the compound streams of gas assumed exactly the shape 
of a tuning-fork. 
2742. When air occupied tlie magnetic field, the division of the stream of hydrogen 
was 0*3 or 0*32 of an inch below the axial line. When oxygen was about the poles, 
then the division of the hydrogen took place as far off as 0*55 of an inch below the 
axial line. Hence at these distances the power which tended to make the hydrogen 
pass from the axial line, equatorially in the direction of the radius, was equal to the 
difference of the specific gravity of hydrogen compared with that of air and oxygen 
respectively. At lesser distances the power would be much greater ; and indeed, if 
in any experiment the hydrogen was delivered nearer to the axial line, it was blown 
downwards and away with much force. Calculating with these data, and still 
assuming that the diamagnetic gases receded from the axial line, in consequence of 
the direct action of the magnet and that only, causing them to pass from stronger 
to weaker places of action, I found, as I thought, reason to believe that the more 
diamagnetic gases, occupying the space within the copper box (2739.), might pro- 
bably be expanded at least 6u;^th part of their volume by the magnetic force. Now 
the gauges that I employed were sensible when the fluid in them moved the of 
an inch (2736.), yet that space is only the 2,5b ~ o76 o b th part of the capacity of the chamber, 
and therefore such an expansion as that above would have made it move through 0*4 
of an inch ; a quantity abundantly sufficient to render the result sensible if the funda- 
mental assumption were correct. 
2743. Air was first submitted to the power of the great horseshoe magnet, urged 
by twenty pairs of Grove’s plates in this apparatus (2739.). The fluid moved very 
slightly outwards, as if a little expansion occurred on putting on the magnetic force, 
and returned when the force was taken off. This small effect was found afterwards 
to be due to compression, occasioned by the tendency of the magnetic poles to ap- 
proximate (2734.). 
2744. Oxygen presented exactly the same appearances as common air and to the 
same amount, so that no effect, due to magnetic or diamagnetic action, was here evi- 
dent, but only that of the compression observed in the case of air (2743.). 
2745. Nitrogeti gave exactly the same results as oxygen and air. Now nitrogen is 
probably more diamagnetic than hydrogen, and should therefore have given a striking 
contrast with oxygen, if any positive results were to be obtained. 
2746. Carbonic acid and nitrous oxide gases yielded the same negative results, and, 
as I believe, when the apparatus was in an unexceptionable condition. 
2747. There is at the Pharmaceutical Society an excellent electro-magnet, of the 
horseshoe form, similar in arrangement to our own (2247-), but far more powerful, 
and this through Mr. Redwood I was favoured with the use of, for the repetition of 
the foregoing experiments at the house of the Society. The iron, which is very soft 
and good in quality, is a square bar, 5 inches in thickness, and the medium line is 50 
inches in length. It has 1500 feet of copper wire, 0*175 of an inch in thickness. 
