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that of empyreuma, or of bitumen. Iti this state it is generally known 
by the term mow-hurnt hay. But if the process be allowed to go on, 
the heat soon considerably augiuents, the vapour assumes the form of 
smoke, and, at length, actual flames break forth, and the whole mass 
is presently reduced to ashes. 
The remarkable evolution of heat, in the fermentation I have just 
spoken of, demands an inquiry whether any thing similar ever takes 
place in the process of bituminization ; since, if that be not the case, 
the parallel would so far fail. But, as the process of bituminization 
is carried on out of the reach of our examination, it is impossible, as 
has been already observed, to speak accurately respecting the phe- 
nomena which arise during its performance. The following account, 
however, contained in a letter from Peter Collinson, Esq. to Sii 
Hans Sloane, which I met with among the unprinted papers of the 
Royal Society, preserved in the British Museum, shows that this 
phenomenon may arise dm'ing this process. You will also perceive 
that the learned writer proposed to account for its occurrence in a 
similar manner with that which I have here adopted. 
‘‘ Our newspapers, printed here, mention the burning of Brooks, 
in the Vale of Good Cheap ; but the case is, that some pieces of 
marshy ground, called brooks, from their watery situation, have 
flamed for some time ; and these they have called burning brooks ; 
the parish next adjoining is also called Brooks. The soil is like 
those parts of Cambridgeshire, where the turf is cut, and very often 
under water ; but this dry season has brought it from very wet to 
that degree of moisture which often causes hay to ferment and take 
fire. Accordingly, this fire begins about four feet under ground, 
just above the water (as appears by digging), and so burns up to 
the surface, where it flames out, especially if stirred with any thing ; 
and, according to the quantity of roots and fuel it meets with, it 
leaves strata of black coal, or red ashes. The fire has now burnt 
for several weeks, and is expected to continue till the rain or springs 
VOL. I. c c 
