128 SPONTANEOUS COMBUSTION. 



larger quantities, from different parts of the ocean, utid^r circum- 

 stances that may favour its escape; often adhering to the sides of 

 vessels, or of their oars us they are alternately raistd from the 

 water, and producing a long line, or an extended sheet, of won. 

 derful brilliancy, not unfrequently variegated by every playfulness 

 of colour. 



It appears obvious, moreover, that it is not to one cause only, 

 but to many, that such phenomena are to be ascribed, at different 

 periods, and in different parts of the world. Linnaeus inclined to 

 confine it chiefly to vast flocks of the nereis tribe : but we have 

 already observed, that even at sea, and among living animals, 

 medusas, sapias, pennatulas, pyrosomas, and phloades equally 

 concur : while, on other occasions, the waves appear brilliantly 

 illuminated, and through a very extensive range, without a trace 

 of any living substance whatever, possessed of a luminous power ; 

 and can only acquire their light from the decomposition of dead 

 animal matter. [Pantologia* 



CHAP, IX. 



SPONTANEOUS COMBUSTION. 



IN the preceding chapter we have confined our remarks to sub. 

 stances which spontaneously emit light with little or no increase of 

 sensible heat. In the present we shall have to notice other sub> 

 stances that spontaneously emit heat, and burn, either in conjunc- 

 tion with light, or, as very frequently happens, without any light 

 whatever : in the course of which we shall have to glance at some 

 very remarkable and interesting effects, which to this hour have 

 never been satisfactorily explained. 



Spontaneous combustion, as a general fact, is well known ; and 

 the more common causes are too obvious to be enlarged upon ; we 

 need only refer to friction and its effects, to the heat produced by 

 the slacking of lime when in contact with combustible matter, to 

 the fermentation of hay, of dunghills, and of similar materials 

 similarly disposed. 



But besides these more common causes, eipcrience has shewn 



