114 SOUND. 



and more pure the air; and, consequently, all sound becomes 

 much enfeebled; for, as we have already seen, the denser the 

 air, the louder the sound, and vice versa if there were no 

 air, nature would be buried in the deepest silence. 



MRS. F. 



De Saussure found, at the top of Mont Blanc, that the re- 

 port of a pistol was no louder than a cracker. 



HENRIETTA. 



Then, I suppose, if we were to ascend much higher, sound 

 would not be heard at all? 



MRS. F. 



Yes, it would; for, recollect, so long as air exists, sound 

 can be conveyed. Although very much weakened at such 

 elevations, yet it is very evident that at heights, where the air 

 must be 3000 times rarer than on our earth, sounds are still 

 transmitted. 



ESTHER. 



How can that be determined? 



MRS. F. 



From the sound of meteors having been propagated down 

 to the earth. The meteor of 1714, whose height when it 

 passed across Italy was at least 38 miles, made a hissing 

 noise, like that of fireworks; and, at Leghorn, gave a loud re- 

 port, like that of a cannon. 



FREDERICK. 



I beg your pardon for interrupting you, aunt; but how 

 could the distance of a meteor be calculated? 



By computing the interval of time between the appearance 

 of its explosion in the air, and the time that the sound arrives 

 at the ear. If a gun be discharged at a distance, you know 

 that the flash precedes the report by some seconds; and so 

 lightning always precedes thunder. Now, as we know the 



