IGNIS FATUUS. 139 



motion of a human being through an atmosphere 

 strongly impregnated with those highly inflamma- 

 ble gases, may be sufficient to produce a train of 

 the cold blue flame. It is from the decomposition 

 of animal and vegetable matters that those gases 

 are produced. The quantity of small animals 

 chiefly of the insect tribes, that are continually 

 perishing in marshes by falling from their island- 

 habitations in their rushes and reeds into the 

 water between, is much greater than would readily 

 be supposed ; and when those waters are shallow, 

 and the air and light, in consequence, act power- 

 fully upon them, there are materials and means 

 enough for the production of ten times the num- 

 ber of ignes fatui, that ever were observed. 

 Church-yards are very favourable for their ap- 

 pearance ; and hence probably the reason why 

 they have been associated with spirits, and consi- 

 dered objects of terror, while they are in them- 

 selves not only perfectly harmless, but exceedingly 

 beautiful, especially when seen in lonely places 

 and through between trees. 



