C. Nyrop: Industriforeningen i København, 1838-1888.
Du Moncel: L’éclairage électrique, 1884, page 102.
Electrician, July 8th, 1882.
La lumière électrique, 1883, VIII, page 58.
The most important source is the papers, left by Hjorth, which comprise a considerable collection of drawings, letters, and rough copies of letters written by him. These documents furnish full information, not only of Hjorth’s inventions, but also of his entire reasoning and manner of being. Probably the most interesting of all are his note-books and sketch-books, wherein he used to note down his ideas in English, and which are accompanied by neatly made, coloured sketches. These papers were not accessible to the public until the autumn of 1908, and they are now preserved in the archives and library of the Polytechnic Institute in Copenhagen.
Important contributions to Hjorth’s history have also been obtained from the State Archives, the Archives of the Society of Science, the Archives of the Polytechnic Institute and from the papers left by H. C. Ørsted.
FOOTNOTES:
[1] According to the usual terminology of those times, an »electro-magnetic« machine means a machine driven by electricity, an electromotor, while, on the other hand, a »magneto electric battery«, or a »dry battery« is a machine for producing electricity.
[2] Specification of Patent No. 12295, 1848.
[3] After the publication of my first treatise in the »Elektroteknikeren«, for February 1907, various parties have objected that Hjorth, in his dynamos, did not use the dynamo principle in its purest form, as he had one large, unwound, cast iron magnet. On the contrary, the above-mentioned leaf of his sketch-book shows that Hjorth, as early as in 1851, has used the dynamo principle in its purest from—exactly the same as used by Siemens in 1867—as all the field magnets have been wound cast iron magnets, and the initial current is induced by the remnant magnetism of these magnets. S. S.
[4] This is correct, as long as he uses armatures with but a single winding, because, in that case, the number of armature windings is proportional to the number of steel magnets. Whereas Hjorth is mistaken, when in 1867 he makes the same statement about a machine, where nothing prevents the armature from being fitted with a great number of windings.
[5] Specification of Patent No. 2198, 1854.