TEKRESTFJAL HEAT. 



formation of hail is an effect of sudden electrical changes in clouds 

 charged with vapour ; for there is no instance known of hail which 

 is not either preceded or accompanied by thunder and lightning. 



Before the fall of hail, during an interval more or less, but 

 sometimes of several minutes' duration, a rattling noise is gene- 

 rally heard in the air, which has been compared to that produced 

 by shaking violently bags of nuts. 



Hail falls much more frequently by day than by night. Hail 

 clouds have generally great extent and thickness, as is indicated 

 by the obscuration they produce. They are observed also to have 

 a peculiar colour, a gray having sometimes a reddish tint. Their 

 form is also peculiar, their inferior surfaces having enormous pro - 

 tuberances, and their edges being indented and ragged. 



These clouds are often at very low elevations. Observers on 

 mountains very frequently see a hail cloud below them. 



It appears, from an examination of the structure of hailstones, 

 that at their centre there is generally an opaque nucleus, resem- 

 bling the spongy snow that forms sleet. Hound this is formed a 

 congealed mass, which is semi-transparent. Sometimes this mass 

 consists of a succession of layers or strata. These layers are some- 

 times all transparent, but in different degrees. Sometimes they 

 are alternately opaque and semi-transparent. 



73. Extraordinary reports of the magnitude of hailstones, which 

 have fallen during storms so memorable as to find a place in 

 general history, have come down from periods of antiquity more 

 or less remote. According to the "Chronicles," a hailstorm 

 occurred in the reign of Charlemagne, in which hailstones fell 

 which measured fifteen feet in length by six feet in breadth, and 

 eleven feet in thickness ; and under the reign of Tippoo Saib, 

 hailstones equal in magnitude to elephants are said to have fallen. 

 Setting aside these and like recitals, as partaking rather of the 

 character of fable than of history, we shall find sufficient to 

 create astonishment in well authenticated observations on this 

 subject. 



In a hailstorm which took place in Flintshire on the 9th April, 

 1697, Halley saw hailstones which weighed five ounces. 



On the 4th May, 1697, Robert Taylor saw fall hailstones 

 measuring fourteen inches in circumference. 



In the storm which ravaged Como on 20th August, 1787, Yolta 

 saw hailstones which weighed nine ounces. 



On 22nd May, 1822, Dr. Noggerath saw fall at Bonn hailstones 

 which weighed from twelve to thirteen ounces. 



It appears, therefore, certain that in different countries hail- 

 storms have occurred in which stones weighing from half to three 

 quarters of a pound have fallen. 



