James Lodge Mapple to Faraday   17 June 1854¹

June 17-54

Sir

In reply to yours I beg to state that my plan consists of 3 disks revolving on their centers two of the disks are of hard coke for the deflagration the other disk is of an insulating substance and is plac’d between the coke disks so as to keep them the proper distance apart which distance is adjustable the Coke disks are plac’d on uprights which spring together which springs press them against the insulating disk which is rotated and causes the Coke disks to rotate with it so as they are consum’d the spring’d uprights pressing them against the insulating disk keeps them the same distance apart of course they will get a little nearer as they get smaller but I think the difference will be very trifling and if any deposit takes place on either of the disks a spring scraper can be applied to remove it as the disks rotate I think the apparatus for the burning is complete and the constancy will depend on the battery but at present it needs trying[.]

Hoping you will excuse my lengthy description

I remain Sir | Your Obedient Servant | J.L. Mapple

14 Roslyn St. | Hampstead

To M. Faraday Esqr.