THUNDER-STORMS. 



cribed to the stars. But let the heavens be overcast, let the stars be hidden 

 by an unbroken mass of the most dense clouds, and still a sufficiency of light 

 will be diffused in the open country to prevent any of the difficulty and incon- 

 venience which would attend any attempt to walk in a dark cave, or in an 

 apartment with closed windows. It cannot, then, be doubted that, in the most 

 clouded nights of deep winter, light, proceeding from some source, is diffused 

 through the air. If this light be supposed to be that of the stars penetrating 

 the clouds, it is necessary to admit that the light of the stars in a clear night is 

 greater, in the same proportion as the splendor of the unclouded noonday sun 

 ' sxceeds the light when the firmament is covered with dense clouds. No one 

 ( having the least powers of observation can admit such an assumption ; and if 

 ( it be not admitted, there remains no other explanation of the nocturnal light of 

 ^ a clouded sky, except in the admission that the clouds themselves are faintly lu- 

 minous. 



If the supposition of the self-luminous property of clouds be entertained, the 

 probability that, under varied circumstances of form, density, mutual position, 

 temperature, and many other conditions, which will easily suggest themselves 

 to every mind, clouds may be endowed with this quality in various degrees. 

 The probability, therefore, of the hypothesis which we have just proposed to 

 account for nocturnal light, will be strengthened, if it can be shown that, on 

 particular occasions, clouds have been observed unequivocally and in much 

 higher degrees luminous. 



In a memoir of Rozier, dated 15th of August, 1781, that philosopher states 

 that, being at Bezieres on that day, in the evening, at a quarter before eight 

 o'clock, the sun having gone down, and the firmament being overcast, thunder 

 was heard. At five minutes past eight, it being then complete night, the storm 

 having attained its height, Rozier observed a luminous point above the brow of a 

 hill fronting his house, which gradually augmented in magnitude until it as- 

 sumed the form and appearance of a phosphoric zone, subtending at his eye an 

 angle of about sixty degrees measured horizontally, and having the apparent 

 height of a few feet. Above this luminous zone was a dark space equal to its 

 own breadth, and over that space appeared another horizontal zone, of the same 

 breadth, and about half the apparent length. The middle of each of these zones 

 exhibited a uniform brightness, but the edges were irregular. Lightning is- 

 sued three times from the edges of the inferior zone, but no thunder was audi- 

 ble. The duration of this extraordinary phenomenon was nearly a quarter of 

 an hour. 



Nicholson relates that, on the 30th of July, 1797, at about five o'clock in the 

 morning, he observed the heavens covered with dense clouds, which moved 

 raf idly to the west-southwest. Lightnings played constantly at northwest and 

 southwest, which, after an interval of twelve seconds, were succeeded by loud 

 claps of thunder. The lower parts of the clouds, which were undulated and 

 checkered, exhibited a red light which was very vivid. At one moment, houses 

 placed in front of that which he inhabited had the appearance which would 

 have been produced by viewing them through a deep-blue glass ; at that time, 

 on looking at the clouds, they appeared to emit a blue light. 



Beccaria states that the clouds over his observatory at Turin frequently dif- 

 fused in all directions a strong reddish light, which was sometimes so 

 intense as to enable him to read a page printed in ordinary type. This 

 nocturnal light was especially observed in winter, between successive snow- 

 showers. 



The selfsame luminous quality has been observed in fogs. The dry fog of 

 1783 was described by M. Verdueil, a physician of Lausanne, as having dif- 

 fused at night a light sufficiently strong to render distant objects visible, and 



j iusea 



