Marc Isambard Brunel to Faraday   5 February 1836

Engineering Office Thames Tun[n]el | Feby 5 1836.

My Dear Sir

The Directors of the Thames Tunnel being anxious to provide themselves with the best information on the relative merits of oil and coal Gas, to direct them in their arrangements for the future economical as well as efficient lighting of the Tunnel, in its present unfinished state, I am directed to solicit your opinion on this interesting subject professionally; which if it should be in your power to afford, will confer an obligation on the Board, that will be most gratefully acknowledged.

I take leave to lay before you a letter addressed by Mr Beamish¹ to me, upon the subject, and a copy of the previous report made to the Directors; with some data on the Capacity of the Shaft Tunnel and Ventilator. Also to submit the following queries which will be found to embrace those practical points on which definite observation is sought.

Query 1st Is the Liability of Explosion of Coal Gas, greater or less than that of Oil Gas, and in what ratio?

2d Is Coal Gas of the best quality made from cannel Coal capable of being rendered so free from Impurity as to be placed on an Equality with oil gas, and has it been actually accomplished in practice?

3d If the heat evolved by Coal gas, is compared with its relative illuminating power to Oil gas, - so great as to excite any reasonable apprehension from is use in the Thames Tunnel increasing the quantity of Vapour.

4 Is the quantity of Moisture generated by Coal Gas as compared with its illuminating power to Oil Gas so great as to form a sufficient objection to its use in the Thames Tunnel.

The area of the Shaft of 1520 feet, and being 58 feet to the roadway of the Tunnel containing 88160 Cubic feet.

The area of both Arches of the Tunnel is 366 [square] feet, and being 600 feet in length they contain 219 600 Cub feet.

The Trunk for the passage of the rarified air is 18 Inches Square, giving an area of 2 1/4 [square] feet, and it extends from the extremity of the Working to the flue of the Steam Engine Tin at the Top of the Shaft, into which it delivers; so that a constant current of air exists; there is also a current passing along the Top of the Arches, back from the extremity of the Shaft.

The Number of lights, at present used, is 40 for 9 hours a day.

I am | My Dear Sir | Very Sincerely Yours | Signed M I Brunel

Dr. Farady