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XXVI I r. Further Bemarks on Thunder Storms. Bj 

 Mr. Cornelius VARLEr. 



To Mr. Tillach. 



Sir, OrNCE the period ;it which I sent you eome remarts 

 on a ihunder storm * seen at a distance, J have been nearly 

 iindir a similar storm, and have remarked two adduional 

 effects, which appear to nie to throw some light iijxni this 

 subject. 



Toward the close of a fine day the air grew thick wltb. 

 vapour, but exliibited no visible form of clouds. This va- 

 pour afterwards condensed into thicker masses, with faint 

 flashes of lio;htning about them. The condensation thea 

 went on very rapid, bo that what was only a thick mist be- 

 fore, became, in an hour, a large general mass of clouds; 

 and I could now see clear sky in different parts, thoucrh at 

 the commencement the whole sky was covered with a faint 

 mist. There was now a great deal of liii,htning between the 

 upper and lower clouds, the effect of which was seen 

 through the under clouds in broad, misty, zig-zag flashes; 

 and nearer the horizon were setn large sparks miming along 

 between the clouds to a great distance. The passage of the 

 light was vi^ible all the way, but the spark seen distinctly 

 ;it all the openings. 



During the time this lightning continued tlicrc was only 

 now and then a little thunder, which I think is clearly ac- 

 counted for by an accompanyin,g effect— namely, the con- 

 densation of a very rare cloud into one more dense, but vet 

 quite elastic. The condensation may be conceived to take 

 place bv the closing together of an immense number of 

 small parcels of clouds, as if the parts of a sponae were 

 made to approach by pressure, and thiijrefore with a very 

 >>ol't and gentle vibration. 



But when a spark strikes from the lowest cloud to the 

 earth the condensation must be into rain, (for there is no 

 intermediate .state between that cloud which is already at 

 its lowest density and rain,) therefore the almosphere has 

 to collapse upon solid inelastic j)ariicles of rain, which must 

 produce a sharp clap ; and this every person knows to be 

 the effect, when lightning strikes down iioni over our 

 heads. 



The wind during all the day had hren south-west, but 

 \vhen the storm counnenced the wlml ceased on the north- 



• See page 101 uf tlie pic^cnt Vuluine, 



cast 



