[9] Nuovo Cimento (1865), 19, 378.
[10] Brit. Pat. No. 1668 (1870); Comptes rendus (1871), 73, 175.
[11] Ann. Chim. Phys. l. 322.
[12] Ibid. li. 76. Since in H. Pixii’s machine the armature was stationary, while both magnet and commutator rotated, four brushes were used, and the arrangement was not so simple as the split-ring described above, although the result was the same. J. Saxton’s machine (1833) and E.M. Clarke’s machine (1835, see Sturgeon’s Annals of Electricity, i. 145) were similar to one another in that a unidirected current was obtained by utilizing every alternate half-wave of E.M.F., but the former still employed mercury collecting cups, while the latter employed metal brushes. W. Sturgeon in 1835 followed Pixii in utilizing the entire wave of E.M.F., and abandoned the mercury cups in favour of metal brushes pressing on four semicircular disks (Scientific Researches, p. 252). The simple split-ring is described by Sir C. Wheatstone and Sir W.F. Cooke in their Patent No. 8345 (1840).
[13] By the “leading” side of the tooth or of an armature coil or sector is to be understood that side which first enters under a pole after passing through the interpolar gap, and the edge of the pole under which it enters is here termed the “leading” edge as opposed to the “trailing” edge or corner from under which a tooth or coil emerges into the gap between the poles; cf. fig. 30, where the leading and trailing pole-corners are marked ll and tt.
[14] Such was the arrangement of Wheatstone’s machine (Brit. Pat. No. 9022) of 1841, which was the first to give a more nearly “continuous” current, the number of sections and split-rings being five.
[15] Its development from the split-ring was due to Pacinotti and Gramme (Brit. Pat. No. 1668, 1870) in connexion with their ring armatures.
[16] And extended by G. Kapp, “On Modern Continuous-Current Dynamo-Electric Machines,” Proc. Inst. C.E. vol. lxxxiii. p. 136.
[17] Drs J. and E. Hopkinson, “Dynamo-Electric Machinery,” Phil. Trans., May 6, 1886; this was further expanded in a second paper on “Dynamo-Electric Machinery,” Proc. Roy. Soc., Feb. 15, 1892, and both are reprinted in Original Papers on Dynamo-Machinery and Allied Subjects.
[18] Exp. Res., series i. § 4, par. 111. In 1845 Wheatstone and Cooke patented the use of “voltaic” magnets in place of permanent magnets (No. 10,655).