Faraday to John Phillips   21 December 1850

R Institution | 21 Decr. 1850

My dear Phillips

If I were with you I would ask a word or two about Arches¹ but my thoughts are not definite enough to make me put them down in ink in association with No. 2. The luminous arch & the dark circular segment though not (apparently) concentric have as far as I have seen the same relation to a vertical plane passing North [of] their centres & the observer but is this center of both a fixture for the same evening & the same as regards astronomical North on different nights. No. 3 would perhaps answer the question but if the plane seems to shift at all though slowly it might be observed if looked for[.]

If I had opportunities of observing aurora I should make this experiment. A horizontal needle hung say by cocoon silk. A bar of thoroughly soft iron about 2 feet long in the position of the dip fixed with one end so near one end of the magnetic needle as to affect it a certain amount deflecting it for instance 45˚ or more. It seems to me likely that any horizontal current of Electricity or equivalent derangement of general magnetism might be better shewn by its effect on this bar & through it on the needle than on the needle alone[.] I think also that a similar bar of iron fixed horizontally & perpendicular to the line of the dip & plane of Mag meridian acting on a horizontal needle hung by silk - might tell about streams of Electricity vertical or approaching to verticality - and that both as to the upping or downing of the discharges.

Ever Yours | M. Faraday

John Phillips Esq | &c &c &c

I have made no marks on the paper but intend to keep that MF