Faraday to Jacob Herbert   20 January 1844

Royal Institution | 20 Jany 1844

Sir

I have received the lamps & cottons from Mr Wilkins and have proceeded to try the different varieties of cotton according to your request. In comparison with them I have tried also a portion of French cotton which I brought from the South Foreland lighthouse for that purpose¹[.]

No.1 is bleached cotton of the ordinary character & thickness

2 - the same -- of extra thickness

3 - unbleached cotton of ordinary thickness

4 - the same - of extra thickness

5 - the French cotton

Specimens are sent herewith[.]

Of these cottons the bleached specimens contain less earthy matter than the unbleached and when burnt leave scarcely a trace of ash - the unbleached cotton leaves an ash which is abundant enough to keep in some degree the form of the thread - but in neither case can this affect by its amount the use of the cotton in the lamps[.] Nor do I find in either case that the substances present in the cotton can by their quality affect the burning of the oil in lamps:- The French cotton is like, and as, the unbleached; but in respect to the nature of the material all appear to me equally fit for the purpose of forming wicks in lamps.

I then, having five clean lamps alike in all respects and a sufficient quantity of good oil such as is furnished by the Trinity house to the lights, used these various cottons burning the lamps for 12 and 14 hours together several times in succession; so that the cottons were all burning at once & under the same circumstances: and I have come to the conclusion that under these circumstances the cottons are as nearly as possible alike in their effects[.] This surprised me as I certainly expected some difference between the thick & the ordinary but they burnt for the same time with the same height of flame & charred nearly together; & even at the end of 12 hours, not having been touched in the mean time, presented, as nearly as possible, similar flames. The bleached stout was on one occasion a little the best but on the next it was a little inferior; the difference in both cases being small.

Of course the amount of coal on the top of the thick & thin cottons was different at the end of each trial - but I am judging of the effect on the flame; the larger coal on the thick cotton seemed to give it neither a superior nor an inferior power to the thinner cotton, under these circumstances.

It is very possible that with oils of inferior quality containing more mucilage or gummy matter, thick & thin cottons may cause a difference²[.]

I have the honor to be | Sir | Your Very Obedient humble Servant | M. Faraday

Jacob Herbert Esq | &c &c &c | Trinity House