Faraday to George Biddell Airy   18 February 1854

Royal Institution | 18 Feby 1854

My dear Sir

With respect to all the phenomena described up to A page 4 of the accompanying report¹, length goes for nothing, except as affording surface, and therefore needed no other notice at bottom of page 3. Plates of copper & water would do just as well in association with Gutta Percha; but one would have to adjust the amount of surfaces: thus, with the wire one surface of the Gutta percha is 8300 square feet & the other 33000 square feet: if arranged as plates we must take the mean of these numbers or 20650 as the square feet of Gutta percha in plates 1/10 of an inch thick, which has to be coated on one side with copper sheathing & on the other with water. So a hundred sheets of such gutta percha each 14 feet by 15 feet or thereabouts, arranged in any of the many ways by which their surfaces could be coated with metal & water, so as to form a Leyden arrangement, would answer the same purpose as the 100 miles of wire[.]

In the phenomena described after A, length goes for much, and is referred to pp 6, 8 10 &c as you will see by the marginal ink numbers 1, 2, 3, 4²:- and if you wish to see the reasoning more developed I must refer you back to the Philosophical Transactions for 1838 and especially to paragraphs 1328, 1330, 1331, 1334³ of the Experimental Research there printed.

In the latter results, described after A, where induction effects are combined with that effect due to length of wire which may be indifferently considered as either conduction or retardation, the induction effect is distributed along the wire; not being equal in every part as in the previous experiment, but diminishing in amount from the battery to the earth; but all such variations are evident at a glance & I need say no more about them[.]

As to the double or treble throbs, preparations for their observation with a view to the determination of their character would require great care. I saw nothing which struck my mind as indicating any thing which was not referable to momentum of the needles, disturbance of their polarity, - trembling contact, & other circumstances; all of which would have to be sought for & then cleared away, before I should be able to draw any conclusion in favour of a resolution of one pulse of power into several, by simple length of wire. The expansion of the time. i.e. the production of a slow action in the distance by a quick action at the battery end was clear enough, and is referred to page 9 fig 5⁴; briefly it is true, but I thought the point too evident to need many words[.]

Ever My dear Sir | Very Truly Yours | M. Faraday

The Astronomer Royal | &c &c &c