Chap. 6.] "Dffcrfytion of a Thunder Storm. 347 



* Thunder ftorms/ fays Beccaria, ' generally hap- 

 pen when there is little or no wind, and their firft ap- 

 pearance is marked by one denfe cloud, or more, in- 

 creafing very faft in fize, and riling into the higher 

 regions of the air; the lower furface black, and nearly 

 level, but the upper finely arched, and well defined. 

 Many of thefe clouds feem frequently piled one upon 

 another, all arched in the fame manner j but they keep 

 continually uniting, fwelling, and extending their 

 arches. 



' At the time of the rifing of this cloud, the at- 

 mofphere is generally full of a great number of fepa- 

 rate clouds, motionlefs, and of odd and whimfical 

 fhapes. All thefe, upon the appearance of the thun- 

 der cloud, draw towards it, and become more uniform 

 in their fhapes as they approach, till coming very near 

 the thunder cloud, their limbs mutually ftretch towards 

 ene another; they immediately coalefce, and together 

 make one uniform mafs. But fometimes the thunder 

 cloud will fwell, and increafe very faft, without the con- 

 junction of any of thefe adfcititious clouds, the vapours 

 of the atmofphere forming themfelves into clouds 

 wherever it pafles. Some of the adfcititious clouds ap- 

 pear like white fringes at the fkirts of the thunder 

 cloud, but thefe keep continually growing darker and 

 darker as they approach or unite with it. 



f When the thunder cloud is grown to a great fize, 

 its lower furface is often ragged, particular parts being 

 detached towards the earth, but ftill connected with the 

 reft. Sometimes the lower furface fwells into various 

 large protuberances, bending uniformly towards the 

 earth. When the eye is under the thunder cloud, 

 after it is grown larger, and well formed, it is feen to 

 fink lower, and to darken prodigioufly, at the fame 

 time that a number of adfcititious clouds (the origin of 



which 



