Electricity.
After Faraday, in 1831, had discovered how an electric current might be produced by means of a magnet, many people busied themselves by trying to put this invention into practical use, and numerous attempts were made to construct electro-magnetic and magneto-electric machines for useful purposes.
No wonder that these efforts attracted Hjorth’s attention, and, as early as 1842, he had drafted an electro-magnetic machine, consisting of a stationary circle of magnets, whose poles were directed against the poles of a moveable circle of magnets. In 1843 this sketch was deposited with the Royal Scientific Society, but the sketch itself, as well as the explanation belonging to it, are very incomplete.
In the month of April, 1848, Hjorth made a petition to the government for a subvention of 200 rixdollars, in order that he might go to England to get an electro-magnetic machine[1] designed by him, made there. Hjorth had noticed that, in a piece of iron encircled by an electric current, the magnetism only to a certain extent would increase, with the strength of current, there being a point of saturation for the iron. When this point has been reached, it will be of no use to increase the intensity of the current, since the magnetism will not increase any further. On the basis of this observation, Hjorth had constructed his machine, but he had confided the details thereof only to Professors Ørsted and Forchhammer. In the report on Hjorth’s petition made by these two professors to the Board of Trade, they, curiously enough, take exception to the above-mentioned observation by Hjorth, while its correctness will now be acknowledged by any electrician. These professors, however, advised that Hjorth’s petition should be granted, using this liberal argument, worded by Ørsted: »Regarding the petitioner’s new electro-magnetic machine, we must state that we find it quite ingenious, and although we are not convinced that it will produce remarkable effects, we should consider it useful to have a working model executed. Having during so many years worked for this case, the petitioner might perhaps, by the execution of such a model, be enabled to make some further invention, which would bring him nearer to the goal. Indefatigable zeal has often accomplished its purpose, where science had to declare the means at first used, to be entirely inadequate, but where, by continued work, entirely different means, previously unknown to the inventor, were found. Inasmuch as the sum of 200 rixdollars asked for is so small, we find it advisable to grant the subvention. Still we cannot refrain from remarking that the petitioner’s machine may just as well be made here as at any other place«.
Thus the discoverer of electro-magnetism cleared the road which was to lead to the most beautiful application of electro-magnetism, that application which, before all others, has been of radically reforming importance during the last half century, thereby throwing double splendor on Ørsted’s name.
Soon after his arrival at London, in the summer of 1848, through a firm which he knew from an earlier period of his life, Hjorth made the acquaintance of a nephew of Bramah, the renowned mechanician and inventor of the Bramah-lock. Hjorth’s invention was then laid before a friend of Bramah’s, a civil engineer named Gregory, who had made the study of magnetism his specialty. Gregory at once persuaded Bramah to bear the expense of making a machine, and of securing patents in England and several other countries, on condition that the expected profits should be divided between him and Hjorth. Later on, B. Taylor and Normann Innis were taken in as partners, paying together £1000, and then Charles Stovin (£600) and Robert Broad, of the Henley Iron Works (£500). Two machines were now made, according to Hjorth’s directions, by the firm of Robinson & Sons, Pimlico, London. One of these is shown in [Fig. 1], and is apparently quite an ingenious imitation of the steam-engines of those days. C is a movable, A a fixed electro-magnet. Their peculiar shape, involving several conical pins fitting into corresponding cavities, was thought to be advantageous for the distribution of the effect of the magnetic force over a longer stroke. The »piston« C, reciprocating up and down, drives a crank shaft having two opposite cranks. To either of the cranks there is a corresponding group of magnets. An eccentric fixed on the shaft, moves a »slide valve«, alternately closing the circuit of one or the other of the two groups of magnets. When the one piston is at its lowest position, the circuit of the other group of magnets is closed, and its piston is attracted, until it reaches its bottom position; then the current is shifted, and the other piston attracted, etc. In order to avoid the formation of sparks at the circuit breaker, an ingenious device was provided, closing the current of one group of magnets, immediately before that of the other one was broken. The first machine was made with a 4 inch stroke, the next one with 13 1/2 inch stroke. The magnetic attraction per square inch of the piston, had about the same magnitude as the pressure per square inch in the low pressure steam-engines of those days. The patent application was filed in London as early as in October 1848, and it was granted on the 26th of April 1849[2]. On the 21st of September, the same year, Hjorth obtained a fifteen year monopoly in the kingdom of Denmark, to manufacture machines, utilizing electro-magnetism as motive power in the above described manner.
[Fig. 1. Hjorth’s Electromotor.]
The larger of the machines here referred to was shown in action to several technical experts, and created considerable sensation, especially on account of the great length of stroke attained—13 1/2 inches—and the uniform motion of the machine. The machine is mentioned in »Mining Journal«, for the 5th of May, and 16th of June 1849, and an extract of these articles is published in the »Flyveposten« for the 3rd of July the same year.
Hjorth was invited to show the machine at the Royal Society, and at the annual meeting of the Society of Civil Engineers, of which he was a member. It was exhibited at the Universal Exhibition in London, in 1851. In the catalogue it was highly commended, and it received the only prize-medal awarded to electrical machines.
There was, however, one essential obstacle to the practical use of this machine, namely the lack of means for cheaply producing electricity in the quantities required by the electromotor. Wet batteries were expensive to use, and if the machine were to become useful in practice, a powerful »dry battery« would be a necessity. Most of the then known machines producing electricity, were fitted with permanent steel magnets, and as the point of magnetic saturation of steel is low, these machines were unable to produce any considerable quantities of electric energy. Hjorth therefore imposed upon himself the task of building a dry battery. His sketch-book from 1851 is full of new schemes for such batteries and improvements on those already existing (Woolrich’s, Elkington’s and Paine’s). From this it appears, among other things, that he was fully aware that, when the spools suddenly entered or left the field, difficulties would arise in the commutation, and he therefore improved the machine by bending the field magnets, obtaining thereby a gradually increasing and decreasing field, the same thing which is, nowadays, attained by using pointed or obliquely cut pole-shoes.—It would be very tempting to study more closely these sketch-books with their neatly colored drawings, showing how many different ideas have been fostered by him, before the actual production of the first dynamo, in 1854. Most of the descriptions and notes have been written in the English language, which he used almost as readily as his native tongue. On the 1st of May, 1851, Hjorth writes in his sketch-book, beside a sketch of a machine having copper discs for armature conductors and cast iron electro-magnets: »By passing the current on the said way round the Electromagnets, these will of course be excited in proportion to the strength of the same, and the more they are excited, the more will the discs be influenced by the magnets, a mutual action thus taking place«.
So it appears that Hjorth, as early as on the 1st of May 1851, with perfect clearness, has pronounced the dynamo-electric principle.
Under the date of June 24th, 1851, we find sketched out another beautiful idea for the construction of a dynamo. It must be regretted that this machine has not been executed, as it would certainly have proved superior to his dynamo of 1855, which has many points in common with this project. [Fig. 2] shows a reproduction of this page of the sketch-book. There is no descriptive text to this sketch, only at one side of the drawing, these very significant words are written: »Magneto-Electric arrangement with mutual action«. All the six powerful held magnets are of cast iron, and they are wound so as to be magnetized by the current, produced by the dynamo itself[3].
[Fig 2. Facsimile of a Page of Hjorth’s Sketch Book, June 24th 1851.]
In November, 1851, Hjorth returned to Copenhagen, and here he continued what he had commenced in England. In May, 1852, he deposited with the »Society of Sciences« some papers, signed by Professors Scharling and Forchhammer in December, 1851. These papers contain two descriptions, written in English, and two drawings of »dry batteries«. These consist of 3 or 4 circular rows of vertical steel rod magnets, placed one above the other, and disposed round a vertical shaft, carrying 2 or 3 circular rows of armatures. Each armature consists of a piece of soft iron, and is wound with a strip of copper, in a special manner. There are, in each row, as many armatures as magnets. The hollow shaft, as well as the magnets, which are fitted with shoes of soft iron, are wound, and encircled by the current produced in the armatures. With regard to the magnetic arrangement, this machine comes very near to the one patented by Brett in 1848, and it will be noticed that it cannot be said to be constructed according to the dynamo principle, as the »mutual« action plays no important part, the magnets being permanent steel magnets, hardly adapted to receive much extra magnetism by the current of the machine. Hjorth points out, as the novel feature of these machines, the division of the steel magnets into many small ones, with an armature corresponding to each magnet. Hereby he claims, for the same weight of the steel magnets, a larger capacity of the machine than if he had used fewer, but larger steel magnets[4]. The machine is fitted with a commutator for direct current.—In March, 1854, the sketch-book contains another sketch of a dynamo, with clear indication of the dynamo principle, approximately as it was patented on the 14th of October the same year[5]. This sketch is reproduced in [Fig. 3]. The machine has two permanent cast iron magnets and two electro-magnets. The armature cores are fitted with oblique pole-shoes. The description is very brief and contains the same as the patent specification.
[Fig. 3. Facsimile of a Page of Hjorth’s Sketch Book, March 1854.]
In 1853 Hjorth negotiated with a certain Dr. Watson, who had constructed a »dry battery« by means of which Hjorth had meant to drive his electro-magnetic machine. The object of their negotiations was to buy out Hjorth’s above-named partners, and to form a new company for the purpose of exploiting the above-mentioned two machines. The partnership, however, was not realized, and in spring of 1854, Hjorth himself commenced to have a 3 HP battery built in Copenhagen. The machine was fitted with cast iron magnets, and in all probability it was similar to the project of March 1854, and agreed with the patent of October, the same year.
This patent specification reads as follows: »The main feature of this battery consists in applying one, two, or several permanent magnets A, of cast iron, and shaped as shewn in the drawing (Figs. [4] and [5]), in connection with an equal number or more electro-magnets B, shaped as indicated in drawing, in such a manner that the currents induced in the coils of the revolving armatures are allowed to pass round the electro-magnets; consequently, the more the electro-magnets are excited in the said manner, the more will the armatures C be excited, and the more electricity of course induced in the respective coilings; and while a mutual and accelerating force is produced in this manner between the electro-magnets and the armatures, an additional or secondary current is at the same time induced in the coiling of the electro-magnets by the motion of the armatures, the said current flowing in the same direction as that of the primary current, after having passed the commutator. The direction of the current induced in the coils of the armatures will, of course, be reversed according to the change of the respective polarities, and the commutator D is therefore applied for the purpose of causing the current to flow constantly in one direction«. Then follows a description of the commutator of the dynamo. Finally the pole-shoes, or false poles, provided on the magnets as well as on the armatures, are mentioned. He points out that the false poles have on the side of attraction, a long straight edge, as distant from the centre as possible, while on the side of separation, either one has a sharp point, nearer to the axis of revolution, »all with a view to avoid reactionary currents, and at the same time to facilitate the motion of the armature«. »While steel magnets also may be applied instead of cast-iron magnets, the permanent magnets may be coiled like the electro-magnets, which also will serve to make them more permanent«.
[Fig. 4. Hjorth’s Dynamo 1854.]
[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.