THE EARTH. 237 



When these terrors have ceased, with which, however, the 

 natives are familiar, meteors of another kind begin to make their 

 appearance. The intense beams of the sun darting upon stagnant 

 waters, that generally cover the surface of the country, raise va- 

 pours of various kinds. Floating bodies of fire, which assume 

 different names, rather from their accidental forms than from any 

 real difference between them, are seen ^vithout surprise. The dmco 

 volans, or flying dragon, as it is called ; the ignis fatuus^' or w-.r,:- 



• The t^is fataus, or wnll-o'-the-wisp, most philosophers are agreed, 13 

 caused by some volatile vapour of the phosphoric kind, probably the phos- 

 phoric hydrogen gas. The light from putrescent substances, particularly 

 putrid fish, and those sparks emitted from the sea, or sea- water when agitat- 

 ed in the dark, correspond in appearance with this meteor. Sir Isaac Newton 

 defines the ignis fatuiu to be "a vapour shining without heat," and it is 

 Usually visible in damp places, about dunghills, burying-grouuds, and other 

 situations which are likely to abound in phosphoric matter. A remarkable 

 ignis fatuus was observed by Mr Derham, in some boggy ground between 

 two rocky hilla. He was so fortunate as to be able to approach it within 

 two or three yards. It moved with a brisk and desultory motion about a 

 dead thistle, till a slight agitation of the air occasioned, as he supposed, by 

 his near approach to it, caused it to jump to another place ; and as he ap- 

 proached, it kept fiying before him. He was near enough to satisfy himself 

 that it could not be the shining of glow-worms or other insects — it was one 

 uniform body of light. M. Becc.aria mentions tiro of these luminous appear. 

 anc*s, which were frequently observed in the neighbourhood of Bologna, 

 and which emitted a light equal to that of an ordinary faggot. Their motioDD 

 were unequal, sometimes rising, and sometimes sinking towards the earth ; 

 Bometimes totally disappearing, though in general they continued hoveringf 

 about six feet from the ground. They differed in size and figure ; and indeed 

 the form of each was fluctuating, sometimes floating like waves and drop- 

 ping sparks of fire. He was assured that there was not a dark night in the 

 whole year in wliich they did not appear ; nor was their appearance at all 

 effected by the weather, whether cold or hot, snow or rain. They liave been 

 known to change their colour from red to yellow ; and generally grew 

 fainter as any person approached, vanishing entirely when the observer 

 came very near to them, and appearing again at some distance. Dr Shaw 

 also describes a singular igms fatuus, wliich he saw in the Holy Land. It 

 was sometimes globular, or in the form of aflame of a candle ; and immediate!) 

 afterwards spread itself so much as to involve the whole company in a pale 

 inoffensive light, and then was observed to contract itself again, and suddenly 

 disappear. In less than a minute, however, it would become visible as be. 

 fore, and run along from one place to another : or would expand itself over 

 more than three acres of the adjacent mountains. The atmosphere at this 

 time, he adds, was tliick and hazy. In a superstitious age we cannot won- 

 der that these phenomena have all been attributed to supernatural agency ; 

 it is one of the noblest purposes of philosophy to release the mind from the 

 bondage of imagifiary terrors ; and by explaiaing the modes in which 



