Faraday to Jacob Herbert   26 June 1846

Royal Institution | 26th June 1846

My Dear Sir,

The ventilating system which had been honoured with the approbation of the Trinity House was arranged experimentally & practically for such lamps as were used in the lighthouses namely Argand burners consuming Sperm oil at a certain rate per hour. A ventilating Tube 7/8 of an inch in diameter was found sufficient inasmuch as it neither hastened the combustion in the lamp nor allowed any of its products to escape into the lanthorn. As soon as I made the trials of vegetable oil burned in Mr. Wilkins's lamps which have been already reported to the Trinity Board¹ and with the Idea that such lamps might perhaps be used in the lighthouses I began to consider what might be the relation of the ventilating tubes to them, for it was not likely that the tube which was not too large for a lamp burning a certain amount of oil should be large enough for another lamp burning half as much more oil in the same time & therefore requiring at least half as much more air to be supplied to it and taken from it. I have therefore had one of Mr. Wilkins's lamps put up with a 7/8 of an inch ventilating tube over it and yesterday examined the power of the arrangement[.] As I expected the tube does not take off all the results of combustion a little escapes continually at the side which may be perhaps a tenth of the whole and this by a sudden gust of wind or the opening of a door or other circumstances may be increased occasionally for a moment or two. A tube fit to carry off the products of combustion of the vegetable oil lamps should be at least one inch or 1 1/16 in diameter.

Now I should not think it necessary (on the whole) to change any of the tubes which are already erected even though the lamps beneath them may be changed but I should much regret the future application of ventilating tubes 7/8 of an inch in diameter to lamps burning half as much more oil as the present lamps. In every such case therefore I would beg to recommend tubes 1 1/16 of an inch in Diameter to be applied²[.]

I am my dear Sir | your faithful Servant | (signed) M. Faraday

Jacob Herbert Esqre | &c &c &c