[Fig. 5. Hjorth’s Dynamo 1854. Fragment of the Patent Drawing.]
From the above-named sketch-book notations, and the patent specification, it will be seen that Hjorth, during the years 1851-54, has repeatedly pronounced the dynamo principle with perfect clearness, and that he has utilized it in several projects.
It is worth noting that Hjorth’s so-called »permanent« magnets are of cast iron. This shows that Hjorth has known of remanence, or permanence. He has known that cast iron always possesses some slight magnetism, either induced by the earth magnetism or as a remnant—remnant magnetism—left over from its being magnetized in a coil. It has heretofore been assumed that Siemens was the first to call attention to this property of iron, in his paper in the transactions of the Royal Society, of the 14th of February, 1867.—Thus Hjorth used this weak remanent magnetism in the large cast iron magnets to produce the initial current in the dynamo, which then excites itself.—At the end of the patent specification, Hjorth points out that the remanent magnets may also be coiled (compare [Fig. 2]), and thereby he comes closer to the later dynamo constructions.
Hjorth is quite right, according to the patent specification, in giving the pole-shoes such a shape that the armature is gradually demagnetized, and in stating that the object of this is thereby to avoid reactionary currents, and consequently the formation of sparks; while he is mistaken in believing to be able to facilitate the motion of the armature by giving the pole-shoes a certain special shape, because in that case, the machine would be a perpetuum mobile.
Together with the above-mentioned dynamo, Hjorth had an electromotor made in Copenhagen, essentially similar to the one exhibited in 1851. When in the autumn 1854 the machines were finished, Hjorth was called back to England, in order to continue the work on his inventions. It is not known whether the machines were sent to England or not; at any rate they aroused some interest there, and he had a new and larger dynamo built by Messrs Malcolm & Campbell; of Liverpool, 7 India Buildings, at the expense of Malcolm and others. This machine was patented in 1855[6], and is shown in [Fig. 6], which is reproduced from a photograph. Here, too, the dynamo principle has been followed, but each electro-magnet is composed of one solid and one tubular electro-magnet, the latter enclosing the former, the two together forming a so-called »cup magnet«, a construction which has also been used by later inventors. Hjorth describes the action of the battery as follows: »The permanent magnets acting on the armatures, brought in succession between their poles, induce a current in the coils of the armatures, which current, after having been caused by the commutator to flow in one direction, passes round the electro-magnets, charging the same and acting on the armatures. By the mutual action between the electro-magnets and the armatures, an accelerating force is obtained, which in the result produces electricity greater in quantity and intensity than has heretofore been obtained by any similar means.« At the same time, Hjorth allowed the dynamo patent of 1854 to lapse, it being merely a provisional patent.
[Fig. 6. Hjorth’s Dynamo 1855, from an old Photograph.]
Together with the dynamo patent of 1854, Hjorth secured a provisional patent on an improved electromotor[7], and together with the dynamo patent of 1855, he obtained the complete patent on the above mentioned electromotor, as well as on another construction thereof[8]. The former consisted of hollow, horizontal electro-magnets (cylinders), being of a special shape inside, adapting them to give to an electro-magnetic piston, reciprocating within them, a long and steady stroke. By means of a crank, the stroke was transformed into a rotary motion. The other electro-motor consisted of wheels, with protruding teeth, which were set in rotary motion by the teeth being attracted into hollow electro-magnets.
Hard Times.
In May, 1856, Hjorth returned from England, disappointed. It will be noted that through the electro-motor Hjorth was led to occupy himself with the dynamo machine. The dynamo was built in order to produce motive power for the motor. All the time he was working on these two inventions, it was his firm belief that if he could make the dynamo drive the electro-motor, he would be able to attain a substantial saving in power, get much more power out of the electro-motor than was consumed in driving the dynamo. The machines would, as it were, run automatically. He could not understand, why Dr. Watson was sceptical with regard to this manner of battery action. He intended to install his machines in ships and locomotives, which would then be propelled with a minimum consumption of power. In short, the combination of dynamo and electro-motor imagined by Hjorth was to be a perpetuum mobile. It has certainly been the great disappointment of his journey to England, that this scheme failed.