Faraday to Trinity House   11 July 1837¹

Royal Institution | 11 July. 1837.

Dear Sir

Before giving an opinion on the point submitted to my attention by the Deputy Master² and Brethren of the Trinity Corporation allow me to state the question itself that I may not inadvertently include any error. An Argand lamp with its colourless glass chimney being placed in the focus of a reflector there are two ways proposed or used for rending the rays which issue from the apparatus red the one by placing a pane of red glass before the centre opening of the mirror the other by putting a small red glass globe round the flame & chimney of the lamp and the question is whether the latter arrangement will allow more light to pass than the former the glass of both pane & globe being exactly equal in tint thickness & quality.

My answer is that there will be no difference but that both the coloration & the loss of light will be the same in the two cases, though the circumstances may seem to be so unlike each other[.]

Whether the light be coloured by the glass & then reflected - or first reflected & then coloured the results will be alike in the end - & whether the rays pass through the red glass within half an inch from the flame or six inches or a foot or many feet still the result will be the same.

The use of a red glass chimney in place of the combined action of a red globe & white glass chimney is advantageous as doing away with the obstruction which the white glass interposes & the use of a small globe or a chimney instead of a large pane of glass is also I should think advantageous since they are less liable to accidents & more readily cleaned.

I am | Dear Sir | Your Obedient Servant | M. Faraday