[Sidenote: C. T. and E. B. Bright, 1855.]
We find a further development or modification of the invention of Page and Ruhmkorff, patented by the brothers C. T. and E. B. Bright on 21st October, 1852, and No. 2103 in the year 1855. In the latter of these patents the inventors state what follows concerning the nature of their inventions.
“A section of an induction coil made after this manner is shown in fig. 7, having a very strong effect. The primary wire, of which only a part is shown, is wound on an iron core, and outside is surrounded by an iron cylinder. Both of these are metallically connected by the flanges of the bobbin, which also are of iron. The secondary coil may also be surrounded by an iron tube, and if the resistance of the circuit be extraordinarily great with still more primary coils, or it may be also contained in the same tube as the primary. In cases where it is found necessary to increase the quantity of the electro-magnetic effects, we find that the forms shown in Figs. 8 and 9 are very effectual, and may by varied on the same principle. The iron core in the middle is wound with the primary wire, and is surrounded by the other iron cores, which are fixed into the large flanges of the middle core, and carry the secondary coils. Should still greater effects be required, more primary or secondary coils connected in series with the others may be added outside, in order to produce a greater extension of the poles and a more extensive induction.”
This patent is interesting also for the fact that in it we find a disposition of parts, viz. the arrangement of several induction coils in ranks, and connected with one another in parallel, which nearly 30 years later was taken up and practically used by Gaulard.
Among the patents of the year 1857 there is an English one by Harrison, claiming as its object the passing of a primary current through one or more induction coils, and the connection of the secondary coils with the carbons of an arc lamp. There is nothing remarkable in the description.
The last attempt to use induction coils for industrial purposes is met with in the year 1878. In this year Jablochkoff took out a German patent, which was also carried out in practice. He required currents of very high tension to feed his kaolin lamp; at that time such currents could only be produced by induction coils. He writes as follows in his patent:—