THUNDER-STORMS. 5Q9 



The Abbe FERRARA relates that on the 18th of June, 1763, he witnessed 

 tri-cuspidated lightnings in the clouds which issued from the southern side of 

 Etna during an eruption. 



The German meteorologist, KAMTZ, states that he witnessed on one occa- 

 sion, and one only, tri-cuspidated lightning. 



' ; If the simultaneous destruction of two or more objects in the same locality 

 '{ by lightning could be taken as conclusive evidence of a corresponding sub-di- 

 vision of a single flash, numerous examples might be given of multi-cuspidated 

 lightning. Such grounds are, however, too conjectural to be admitted as the 

 basis of any safe conclusions. 



It is a general opinion that cuspidated lightnings, or lightnings of the first 

 class, are those only by which terrestrial objects are stricken.* 



The lightnings of the second class, or sheet-lightnings, are inferior in the in- 

 tensity, and generally different in the color of their light, from those of the 

 first class. These distinctions are very apparent whenever the space over which 

 sheet-lightning is diffused is intersected by flashes of cuspidated lightning. 

 Sheet-lightning sometimes appears to illuminate the edges only of the clouds ; 

 occasionally, however, it seems to issue from the interior of their mass. The 

 common expression that the clouds appear to open, is strongly indicative of its 

 appearance. 



Sheet-lightning is that which is the most frequent, and every one is familiar 

 with its appearance, many having never seen, or never noticed any other. In 

 common thunder-storms it appears in a thousand cases for one in which cus- 

 pidated, or ball-lightning, is exhibited. 



The flashes of sheet-lightning often appear in very rapid succession, and 

 continue, with interruptions, for many hours. In extreme heat, these flashes 

 succeed each other as rapidly as the flapping of the wings of a small bird, and 

 present a flickering appearance in the clouds which they illuminate. The 

 thunder by which they are accompanied is generally low and distant. 



Lightning of the third class, or ball-lightning, is still more rare in its appear- 

 ance than the zig-zag, or cuspidated lightning. The following instances of this 

 meteor have been collected by M. Arago : 



* If tbe reader has attentively considered the preceding: paragraphs, and what has been elsewhere 

 written on this subject, he will be sensible of the deficiency in the vocabulary of the English lan- 

 guage as regards the effects necessary to be expressed. T here are tliree distinct terras in the French 

 language, Le Tonnerre, L' Eclair, and La Foudre. The first expresses the sound proceeding from the 

 clouds which usually follows the flash of light, and is properly translated by thunder. Tbe second 

 expresses the light which precedes the thunder, and the third expresses the actual mutter, the physi- 

 cal sitosfatu-e, whatever it may be. which strikes terrestrial objects, and produces those effects which 

 are so well known. In English there is, properly speaking, no term corresponding to La Foudre. 

 The terms thunder and lightning are indifferently used to express the same effect as when'we say 

 thunder-struck and struck with, lightning. In French there is also the useful and necessary verb 

 foudroyer, of which there is no better English synouyme than to strike u-ith ligltfning. The temi 

 thunder-bolt corresponds to La Foudre, but it is scarcely admissible into the nomenclature of science. 

 The electric fluid, which is sometimes used to avoid the term thunder-bolt, is faulty, iuaa.imch as an 

 effect familiar to all mankind in all ages, ought not to be expreise-i by a term having imnHxtitUe refer- 

 ence to modern physical science. 



