27 ; 
Indeed, the very considerable disengagement of heat, during the 
decomposition of pyrites, will easily account for the natural accen- 
sion of so combustible a body as coal, if in union with it whilst 
such a process is going on. Thus Dr. Jordan, speaking in his 
Essay on Mineral Waters, of the properties which coals possess, 
when they contain much of the pyrites, or, as the colliers say, coal- 
metal, of heating and even kindling upon the gradual accession of 
moisture, or the affusion of water upon them, states, that several 
such accidents have happened at Newcastle ; and he particularly 
mentions a circumstance of this kind having occurred in London, 
at Puddle-dock. Dr. Plott* relates, that at Ealand, in Yorkshire, 
one Wilson having piled up many cart-loads of pyrites in a barn of 
his own, for some secret purpose, perhaps to extract the gold ; the 
roof being faulty, and admitting rain-water to fall copiously in 
among them, they first began to smoke, and at last to take fire, 
and burn like red-hot coals, so that the town was considerably 
alarmed. 
To effect the dissipation of a considerable portion, if not the 
whole, of the inflammable matter, from vegetable and bituminous 
masses, such a degree of heat may perhaps be sufficient as may 
neither render the mass, nor the vapours which evolve from it, 
luminous, but during the darkness of the night. The phenomena 
described in the following account, related by John Stephens, M. A. 
in the Philosophical Transactionsf , seems to point out such a gra- 
dual decomposition of pyrites ; and which, by charring the included 
combustible matter, might be competent to the formation of the 
peculiar coal here treated of. Mr. Stephens says, that in the 
month of August, 1751, the air, having been for some time remark- 
ably hot and dry, was changed of a sudden by a heavy fall of rain, 
* The Natural History of Staffordshire, by Dr. Thomas Plott, p. 142. 
t Philosophical Transactions, vol. Hi. p. 119* 
