Peter Theophilus Riess to Faraday   20 March 1855

My dear Sir

The interesting experiments of Mr. Latimer Clark, published under the aegis of Your great name in the last number of the Philos. magazine¹, together with the consequences drawn by the late Melloni, incline me to the following remarks. Melloni’s conclusion, the velocity of propagation of the electricity to be independent of the electric density, appears to me not justified; on the contrary I incline to the view, that the velocity of electricity is proportional to its density. I believe, I have experiment to corroborate the result deduced by me from inquiries made sixteen years ago on the production of heat in the circuit of the Leyden battery. Then I maintained that the time of discharge of the battery is directly proportionate to the quantity of accumulated electricity, and inversely proportionate to its density. I have represented the time of discharge of the battery in §.436 of my treatise on frictional electricity by the relation b(1/b + V)q/y². The letter b and V depend of the nature of the metallic conductor, q is the quantity of electricity accumulated in the battery, y its density. It is evident by this expression, that, if the quantity of electricity 1 is brought in one jar and the quantity 2 in two jars, if the discharge of the first jar through a given conductor results in the time 1, the two jars will be discharged in the time 2; that on the contrary the time of discharge will remain 1, if the quantity 2 is accumulated in one jar. In the last case q as well as y have been duplicated, and the value of the fraction q/y is not altered. This case, I believe, furnishes an explanation of Clark’s experiments. If we make the supposition, very plausible considering the great velocity of electricity, that the chemical action in Bains³ telegraph will commence only after the transmission of the whole quantity of electricity evolved at each instant on each pole of the voltaic battery, the telegraph in Clarks experiments began to mark, when, by using the smaller battery, a certain quantity with certain density had passed the telegraph, and, by using the larger battery, when an nfold quantity with partly the nfold density had passed the telegraph. The law above announced, though found for the Leyden battery and hypothetically referred to the voltaic battery, informs that the time of discharge of the battery is the same in both cases, and it follows that the time for the progress of the discharge from the nearer to the further end of the long wire must be the same both for the smaller and the larger battery.

You remark, my dear Sir, that Melloni shortly before his death, was about to publish facts, by which he hoped to demonstrate clearly the errors of conclusions, arrived at by Coulomb, Poisson and others respecting electrostatic induction⁴. It is to be regretted, that he has really accomplished his intention. He sent on that subject a letter (dated 12 July 1854) to Baron Humboldt, and Humboldt communicated it to the Academy of Berlin, where I was acquainted with it⁵. Melloni undertakes to prove, that an inducteous body, during the presence of the inductric, receives only electricity of the same kind with the latter, and that the electricity of the opposite kind is only evolved after the remotion of the inductric body. Just the same view has been pronounced long ago in Germany, but has been left as wholly untenable and as produced only by misinterpreted experiments.

Melloni has communicated these inquiries also to Mr. Regnault, and You will find them published in the Comptes rendus de l’academie de Paris vol. 39 p.177⁶[.]

I have the honour to remain with the greatest veneration | Yours P. Riess

Berlin 20 March 1855. | Spandau Strasse

Address: Professor Michael Faraday | member of all Academies of Science | London | (royal Institution).