There is a wide interval between the external characters of the lignites and of coal, and though we cannot presume to state the period which Nature has used in her operations, nor during how long a space the causes have continued to act, before the vegetable matter has undergone its ultimate change into coal, nor therefore whether the long continued agency of water and pressure may not have produced the required changes, yet, since Philosophers of high reputation have supposed that fire has been a probable cause of this conversion, and that this theory is supported by considerable evidence in some analogous cases, it is our duty to examine by experiment, what effects conducing to this end may result from our limited trials. The foregoing experiments show that the fire of our furnaces does not convert wood into bitumen, and the processes of Nature seem to prove that water can produce this effect, and that jet, the bituminous lignite which approaches nearest to coal in its chemical characters, is the result of this action. Yet there is an interval between jet and coal as I have already observed, requiring explanation. The chemical characters may be identical, but the mineralogical resemblance is still wanting. It is possible that the agency of fire may account for this ultimate change, and that its action on beds of lignite and peat has converted not wood but vegetable matter already bituminized by water into coal. Pursuing this train of investigations I was induced to try if jet, the most perfectly bituminized lignite, could by the application of heat under pressure be converted into coal. For this purpose I introduced powdered jet into gun barrels, placing it between two portions of rammed Stourbridge clay, with the view of absorbing a part of the distilled petroleum when it might be formed in greater quantity than was requisite for the success of the experiment, and where by its conversion into hydrogen, it might endanger the bursting of the appa-
