METEOROLOGY. 55 



It is also necessary for the deposition of dew, that the 

 temperature of the body on which it may be formed 

 should be below that of the atmosphere ; the vapour in 

 contact thus becomes condensed, and the aqueous par- 

 ticles settle thereupon. Egypt and many other countries 

 very much abound with dews, for the air is too hot in 

 the day-time to constipate the vapours into clouds ; it, 

 therefore, never rains, but the nights being remarkably 

 cold, the vapours are condensed in Dews. 



If the temperature of the air be low, the vapours will 

 sometimes become frozen before they are formed into 

 drops ; their specific gravity is then greater than that of 

 the air, and they descend in Snow. 



If the vapours are united into drops, and become frozen 

 in falling, they are called Hail.* As Hail is often found 

 to accompany thunder and lightning, it is considered an 

 electrical phenomenon. Showers of hailstones of extra- 

 ordinary magnitude have occasionally taken place, more 

 particularly on the Continent, which have carried with 

 them death and devastation to an incredible amount. A 

 most violent storm of hail fell on the army of Edward 

 III., near Chartres, in France, when the hailstones were 

 so large that they killed 6000 of his horses, and 1000 

 of his best troops. At Antwerp, in Holland, in 1776, 

 hailstones fell as large as hens' eggs, and weighed three 

 quarters of a pound ; horses were killed, and the fruits 

 of the earth destroyed. In France, in 1785, one hundred 

 and thirty-one villages and farms were laid waste by a 

 dreadful storm of this nature. 4 In order to prevent the 

 destruction occasioned by hail-storms, which often de- 

 stroy the vintage in the south of France, an instrument 

 called a paragrele has been invented, by means of which 

 the electricity of the atmosphere is said to be disturbed, 

 and hail- storms rendered less severe. 



Sometimes a luminous circle appears round the body 

 of the sun and moon, this is called a Corona or Halo, 

 and is attributed to the refraction of the rays of light in 

 passing through the vesicate of a thin vapour. 



* Hailstones are said to fall with a rapidity of at least 60 feet in 

 a second. 



