|Recipient Location||Mrs Burnside's, Castle Gate, Nottingham|
|Transcript or Index||The chief difficulties of Magnetism seem to be its permanency; its having no tendency to equalize itself while the circuit is continued, its having no effect on the senses, and no loss of power by communication; in the latter property, and in its permanency, it seems however to be approached by the Electric column of de Luc. – It was at first believed that Galvanism differed from electricity, till Volta in the first visible spark which he obtained established their identity. This was not till 1800 – and the progress of the Science has since been astonishing. The peculiarity of Voltaic Electricity consists in its effects being obtained from Conductors, which were before supposed incapable of exhibiting them. The weakest Voltaic Battery affects the Needle more than the strongest electrical Machine. There is still a doubt whether the Auroras be an electrical or Magnetic phenomenon. Mr Dalton has observed that the luminous flashes are coincident with the dip of the Needle – Temperature is perhaps connected with Electricity as electricity is with Magnetism. Thus water in a state of vapour is a perfect conductor, an imperfect conductor when fluid, and as ice, an electric or non conductor. A bar of copper and antimony united, produces no effect on the needle while at a natural temperature, but if one end be heated and the other in contact with ice, it has been found to produce a variation of no less than 21° 30’. |
[On left side of paper - sketch of square with two sides of antinomy and two sides of bismuth needle inside and with lamp outside to the right]
If an open metallic square, formed of two bars of antimony and two of Bismuth, have a needle suspended within it in the direction of the Magnetic Meridian, and the temperature of one half the Square be elevated by the application of a spirit lamp or other means, the Needle will change its direction. In like manner if a strong brass wire be twisted round a bar of antimony, it has no effect on the needle when cold, but changes
[In left side of paper in bottom corner – sketch of bar of antinomy with brass wire connected near ends in shape of semi-circle]
its direction materially if one end be heated and the other cooled. These experiments countenance the idea that the diurnal variation of the Needle arises from the alternate attractions of heat and cold in the Eastern and Western Hemispheres, as they are daily exposed to the heat of the sun, and daily withdrawn from it. Dr Lorimer carries this idea still farther, in attempting to account for the greater or progressive variation from the motion of the earth in its orbit acting upon the diurnal variation so as to produce an effect similar to the precession or rather retrocession of the Equinoxes, and thus occasion the revolution of the Magnetic Pole.
Mr Millington concluded by exhibiting a mahogany cane of about 12 inches cube, made by Mr James Marsh, a person in a very inferior station in the Royal Academy at Woolwich, who has contrived to comprise in that compass the apparatus for exhibiting all the new experiments in Magnetism and also some of his own invention. He has been lately rewarded for it by the Society of Arts with their Medal, & an additional present of 30 guineas.
So far Mr Millington. Many of the facts you are already familiar with, but I thought it right to give you the old along with the New, that you might see the manner in which he brought them together, and make your own inferences. I am aware I have done it but clumsily, having been delayed till much of the freshness of my memory was worn off, but I think you will agree with me that the whole seems to lead towards the deduction that Magnetism is, like Galvanism, only another modification of the Electric power, or perhaps only another branch of Voltaic Electricity itself. If Electricity and Magnetism should turn out to be distinct agents, I then think that their powers must be in some degree combined in the Voltaic Battery. But perhaps I am getting out of my depth here, & so I will stop.
Thursday. June 19th – 1823
Mr Millington continued the subject of the diminution of the power of Magnetism by heat. Professor Cummin of Cambridge, and several of the Continental Experimentalists establish the fact of the variation of the Needle even so much as 70° in the half heated Square, etc; but it was remarked that in all these instances two metals were employed so that it was possible the affection of the Needle might not be a magnetic phenomenon, but simply the result of Voltaic Electricity. A farther examination however removed this doubt. Mr Ritter first noticed the tendency of the North Pole of the Magnet to the positive Pole of the Battery, as also the fact that the South Pole of Magnetized iron is most liable to rust, as is the North End of a steel Magnet. It is now proved that every metal is capable of acquiring the Magnetic virtue under peculiar electrical circumstances, and though the phenomena of Animal Magnetism rest upon his assertion only, and have been the cause of much imposture and ridicule, it is evident that Magnetism must exert some chemical agency, since it is always the acting Pole which is most liable to rust.
Professor Oërsted [Ørsted] of Copenhagen, in the years 1806 & 1807 published some remarks in which he hazarded the idea that Magnetism was only a modification of Electricity. The Galvanic or Voltaic Electricity being only more latent than the common electricity, and Magnetism more latent than either. <(My idea you see! I shall get quite proud!)> He continued to make experiments on the subject till 1819, when his industry was rewarded by the important discovery, that metals become Magnetic while the curr[ent] of Electricity is passing through them, but lose their power the mom[ent] the cir[cuit] is broken. All this you may remember I either wro[te] you to [Am]erica or have given you since, so I need not take up your time and my own with repeating it here. As the effect takes place equally through Glass, it cannot be electrical. If the electricity enters above the needle, and parallel to it, that end which is next the Negative Wire invariably moves towards the East if the Electricity be introduced from below, the end next the negative wire moves to the West. Mr Millington thought this fact of so much consequence as to placard in large letters “The Pole above which Negative Electricity enters is turned to the West – Under which to the East.” – If the electricity approach on the same Plane the Needle dips. It might be supposed that these effects were electrical, but they cannot be produced with a brass needle consequently are purely Magnetic. These experiments of Prof. Oërsted have been repeated and extended by Sir Humphrey Davy, Mr Faraday, & Prof. Cummin. M. Ampère reduces all Magnetic phenomena to causes purely electrical. He found that the needle placed by the side of a Voltaic trough or Battery in action, obeys the direction of its action as well as the connecting wire. That is to say that if placed by the side of a Battery it will assume a particular position, according to the direction of the electric action, without a contact, or being made part of the Circuit. Any metal employed to connect the two poles of the Battery becomes magnetic so that the Magnetic effects appeared to be a mere modification of electricity, one electrical pole attracting, & one repelling the Needle. M. Ampere made an experiment by passing electricity through two parallel pendulous wires. When the electricity is passed through both in the same direction they run together, but repel under contrary electricities. The union of the two thus seeming to suspend the Natural law both of electricity and Magnetism, as in this case the attraction is exhibited by the similar poles. The Attractive power which the Voltaic wire exerts upon iron filings is evidently not electrical, as it is does not take up other light substances. In this Stage of the Science it was taken up by Sir Humphrey Davy who on the 16th Novr 1820 read to the Royal Society his paper on Electro Magnetism. It occurred to him that if the effect were really Magnetic the Voltaic Battery ought to be capable of communicating Magnetic virtue to steel. Small magnets had indeed been made by passing repeated shocks of electricity through them, but the effect was weak & uncertain and might be influenced by various causes, to this point therefore he directed his mind, and found the Magnetic influence not to be in the direction of the wire but at right angles to it. The Needle did not become Magnetic if itself employed to form the circuit – but if laid across [narration continued on next letter D8760/F/FSJ/1/1/30]
More Science, and matter less Scientific tomorrow.
ever yours affectionately
Eleanor Anne Porden.
Captain Franklin, R.N.
Y 20 JU 1823