Charles-Gaspard De La Rive to Faraday   24 September 1822

Geneva 24th 7bre 1822

Dear Sir

I am quite ashamed for having been such a long time without answering to your kind letters of the last autumn¹, and without thanking you for the charming apparatus which you sent to me by an Italian Gentleman. I was always waiting till I could send to you some piece of scientific news worth your attention, and at last I take the pen without having obtained what I wished for. - You have perhaps seen in the Annales de Chimie in a Letter to Mr. Arago that I had made some experiments to ascertain whether it was possible or not to prove by experiment the existence of Galvanic currents at the Surface of the Earth going from East to West according to Mr Ampère’s theory²: For that purpose I tried to analyse the Rectangle contrived by Mr A. which turning around a vertical axis, and placed in the Galvanic Current, always took a diversion perpendicular to the Magnetic Needle. - I did Show that the diversion did not depend from the Inferior horizontal branch as Mr A. believed, but that it was highly probable that the Rectangle took its direction from the Influence of the two vertical branches. - My Eldest Son³ who is [a] very active labourer [in] that part of the Science, undertook to make a Complete analysis of that Rectangle, and contrived for that purpose an apparatus by means of which it was possible to take away the one after the other any of its branches, and even three at a time, and that without troubling the diversion of the Current - (That apparatus is described in a paper which shall be published in the Biblioth. universelle and of which I shall send you a Copy by the first opportunity⁴) - By means of that apparatus he proved that the horizontal branches were of no use in the production of the Phenomenon of diversion, and that the vertical ones were only necessary for that production. - He found afterwards that a single vertical wire, which may turn around a Vertical axis, when placed in the Galvanic Current always forces itself to the East if the Current is descendent, and always to the West of the Current is ascendent. This experiment as you may see is quite concordant with your views - By means of the same apparatus he has Shown that in the turning circle of Mr Ampere the vertical Branches are of no use whatever, the force produced in the one being destroyed by the equal adversary force produced in the other, but that the whole Phenomenon is depending on the horizontal part of the apparatus, and is the consequence of what you had observed with regard to the horizontal motion of a wire when it receives a Galvanic Current. If such a wire is fixed by one of its extremities it is acted on by parallel forces and it turns round the point to which it is fixed, because, as you have Shown, these parallel forces act in every position while the wire remains horizontal and carries the Galvanic Current. Now in Mr Ampere’s Apparatus you have two (or more) horizontal wires, and as the Galvanic Current arrives in the middle, goes on the right and left side in an opposite direction, of course the parallel forces act on each side of the point of suspension in a direction proper to make the wire turn around the point and thus is produced the rotary motion - These forces are by means of the apparatus put beyond any doubt whatever. - Mr Ampere who came to Geneva this summer has been convinced of their truth and accordingly he has made some alterations to his former supposition. He thinks always that our Globe is surrounded by Galvanic Currents going from East to west, but that their principal energy is at the Magnetic Equator, with that supposition, he may explain pretty well the above mentioned facts. - While Mr Ampere was at Geneve he made in my Laboratory two new Experiments. Having a strong disposition to believe that a Repulsion was taking place in all the parts of a Galvanic Current he contrived to demonstrate that repulsion by Experiment. He took a dish of Earthenware separated in two parts by a piece of glass, the two semicircular portions were filled with Mercury; then he took a piece of wire surrounded with Silk, a part of that wire was parallel to the Glass, and floating on Mercury, the wire passed afterwards on the other side of the glass and had another leg parallel to the first, also on the Mercury, the extremities of each leg were in a Metallic contact with the quick Silver as soon as the Poles + and - were put in each Semicircular portion of the dish the wire was sent back to the opposite side - This experiment has some analogy with yours in which there was a loss of weight⁵, with the difference, that in this the Current is both in Mercury and in the wire, in an horizontal direction, while in yours it is horizontal in the Quick Silver and vertical in the wire <->

Be kind enough Dear sir as to write to me if you have some Scientific news, you will see Dr. Marcet who is coming to Geneva if you had some papers of yours to send me I should be very much obliged to you - At any time if you have such papers be good enough to send them to Messrs. Morris & Prevost ⁶ in the City[.] They will forward them to Geneva -

Believe me Dear Sir | Yours for Ever | G. De la Rive

The other experiment Mr Ampere made, is this - He placed a piece of Copper very near a strong galvanic current without being in contact with it, and he found that when the current was very intense, the piece of copper was through influence, made Magnetic, so that it was attracted or repulsed by a Magnet; as soon as the Galvanic Current ceased, the Magnetic property disappeared⁷.

I have always forgot to thank you for the honorable mention you have made of my little floating apparatus⁸.

You may do what you please of the facts contained in this letter.

Address: Mr Faraday | Royal Institution | Albemarle Street | Londres