James Timmins Chance to Faraday   1 December 1860

Hamstead | Birmingham 1 Dec: 1860

My dear Sir,

I quite think that 20mm for the middle band, & the upper ribs; & 36 aside 11 up for the lower ribs; will be right for the “Smalls” refractors¹.

Your ‘dip’, & the corresponding elevation of the burner, are about right. The latter I make 3 mm; the former (allowing for refraction) being 11 minutes:- without refraction being allowed, it is, as you say, about 12½ min: being more accurately 12’ 50” (without refraction)

If we could always be sure of a really good, middle flame at the ‘Smalls’, I should say 21mm for the focus of the middle band:- but as the flame may often be rather low, it is safer, - so as to ensure the brightest light not being sent to the sky,- to keep to 20mm; thus giving 17mm for the dead level focus, after allowing 3mm for the dip. That is, the Sea-horizon focus, for the middle band, will be 20mm above the burner, as the starting adjustment.

Am I to commence the adjustment of the ‘Smalls’ at once, or shall I wait for my official sanction?

Yours very truly | James T. Chance.

Profr. Faraday &c &c