[ 85 ] 
IV. Experimental Researches in Electricity. — Twenty-seventh Series. By Michael 
Faraday, Esq., D.C.L., F.R.S., Fullerian Prof. Chem. Royal Institution, Foreign 
Associate of the Acad. Sciences, Paris, Ord. Boruss. Pour le Mirite, Eq., Memh. 
Royal and Imp. Acadd. of Sciences, Petersburgh, Florence, Copenhagen, Berlin, 
Gottingen, Modena, Stockholm, Munich, Bruxelles, Vienna, Bologna, 8^c. S^c. 
Received November 19, — Read November 28, 1850. 
^ 33. On Atmospheric Magnetism — continued. 
^ ii. Experimental inquiry into the laws of atmospheric magnetic action, and their 
application to particular cases. 
2969. Believing that experiment may do much for the development of the 
general principles of atmospheric magnetism, and produce rapidly a body of facts on 
which philosophers may proceed hereafter to raise a superstructure, I endeavoured to 
find some means of representing practically the action of the atmosphere, when heated 
by the sun, upon the terrestrial magnetic curves. The object was to obtain some 
central arrangement of force which should deflect these curves or lines as they are 
deflected in a diamagnetic conductor or globe of hot air {2877-), and then apply the 
results obtained by such an arrangement as a partial test to the various cases supplied 
by the magnetic observatories scattered over the earth. At first I endeavoured, for 
the sake of convenience, to attain this desired end by means of a horseshoe magnet, 
employing the lines which passed from pole to pole to disturb and rearrange the 
earth’s force ; but the comparative weakness of the terrestrial force near the magnet, 
and the great prominence of the poles of the latter, gave rise to many inconveniences, 
'A^hich soon caused me to reject that method and have recourse to a ring-helix and 
voltaic apparatus. Considering the new use to which this helix is to be applied, the 
interest of the results, and the instruction that may be drawn from them, I shall be 
excused for being somewhat elementary in the description of its character and 
action. 
2970 . The helix consisted of about 12 feet of covered copper wire formed into a 
ring having about twenty-five convolutions, and being 1^ inch in external diameter. 
The continuations of the wire were twisted together so as to neutralize any magnetic 
effect which they could produce, and were long enough to reach to a voltaic arrange- 
ment, and yet allow free motion of the helix. The requisite amount of magnetic 
power in the helix may be judged of by the following considerations : — Suppose a de- 
clination needle freely suspended ; and then the helix placed at a distance in the pro- 
longation of the needle with its axis in a line with the latter, and with that side to- 
