294 ELECTRIC LIGHT. SECT. XXVIII. 



with sparks of electric light, which were driven rapidly to lee- 

 ward by the wind. Fifteen minutes later an immense mass of 

 lightning struck the mainmast, attended by a violent gust of 

 wind ; and another heavy discharge fell on it a quarter of an 

 hour afterwards. From that time till six o'clock the ship was 

 continually encompassed by sharp forked lightning, accompanied 

 by incessant peals of thunder. Though actually enveloped in 

 electricity, and struck three times, neither the hull nor the 

 rigging sustained the slightest injury. 



When the air is rarefied by heat, its coercive power is dimi- 

 nished, so that the electricity escapes from the clouds in those 

 lambent diffuse flashes without thunder so frequent in warm 

 summer evenings ; and when the atmosphere is highly charged with 

 electricity, it not unfrequentiy happens that electric light, in 

 the form of a star, is seen on the topmasts and yard-amis of ships. 

 In 1831 the French officers at Algiers were surprised to see 

 brushes of light on the heads of their comrades, and at the points 

 of their fingers when they held up their hands. This phenomenon 

 was well known to the ancients, who reckoned it a lucky omen. 



Many substances, in decaying, emit light, which is attributed 

 to electricity, such as fish and rotten wood. Oyster-shells, and 

 a variety of minerals, become phosphorescent at certain tempera- 

 tures when exposed to electric shocks or friction : indeed, most 

 of the causes which disturb molecular equilibrium give rise to 

 phosphoric phenomena. The minerals possessing this property 

 are generally coloured or imperfectly transparent ; and, though 

 the colour of this light varies in different substances, it has no 

 fixed relation to the colour of the mineral. An intense heat 

 entirely destroys this property, and the phosphorescent light de- 

 veloped by heat has no connexion with light produced by fric- 

 tion ; for Sir David Brewster observed that bodies deprived of 

 the faculty of emitting the one are still capable of giving out the 

 other. Among the bodies which generally become phosphores- 

 cent when exposed to heat, there are some specimens which do 

 not possess this property ; wherefore phosphorescence cannot be 

 regarded as an essential character of the minerals possessing it. 

 Sulphuret of calcium, known as Canton's phosphorus, and the 

 sulphuret of barium, or Bologna stone, possess the phosphores- 

 cent property in an eminent degree. 



Multitudes of fish are endowed with the power of emitting 



