178 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
195. The twisted copper and iron (touching- each other nowhere but at the 
extremity) was then passed between the poles of a powerful magnet arranged 
horse-shoe fashion (fig. 32.); but not the slightest effect was observed at the 
galvanometer, although the arrangement seemed fitted to show any electrical 
difference between the two metals relative to the action of the magnet. 
196. A soft iron cylinder was then covered with paper at the middle part, 
and the twisted portion of the above compound wire coiled as a spiral around 
it, the connexion with the galvanometer still being made at the ends A and B. 
The iron cylinder was then brought in contact with the poles of a powerful 
magnet capable of raising thirty pounds ; yet no signs of electricity appeared 
at the galvanometer. Every precaution was applied in making and breaking 
contact to accumulate effect, but no indications of a current could be ob¬ 
tained. 
197- Copper and tin, copper and zinc, tin and zinc, tin and iron, and zinc 
and iron, were tried against each other in a similar manner (194), but not the 
slightest sign of electric currents could be procured. 
198. Two flat spirals, one of copper and the other of iron, containing each 
eighteen inches of wire, were connected with each other and with the galva¬ 
nometer, and then put face to face so as to be in contrary directions. When 
brought up to the magnetic pole (53.), no electrical indications at the galva¬ 
nometer were observed. When one was turned round so that both were in the 
same direction, the effect at the galvanometer was very powerful. 
199. The compound helix of copper and iron wire formerly described (8.) 
was arranged as a double helix, one of the helices being all iron and contain¬ 
ing two hundred and fourteen feet, the other all copper and containing two 
hundred and eight feet. The two similar ends A A of the copper and iron 
helix were connected together, and the other ends B B of each helix connected 
with the galvanometer; so that when amagnet was introduced into the centre 
of the arrangement, the induced currents in the iron and copper would tend 
to proceed in contrary directions. Yet when a magnet was inserted, or a soft 
iron bar within made a magnet by contact with poles, no effect at the needle 
was produced. 
200. A glass tube about fourteen inches long was filled with strong sul¬ 
phuric acid. Twelve inches of the end of a clean copper wire were bent up 
