446 Experiments on the Velocity of Sound. [Book V. 



Some curious experiments were made, relative to 

 the propagation of found, by Meflieurs de Thury, 

 Maraldi, and de la Caille, upon a line fourteen thou- 

 fand fix hundred and thirty- fix fathoms in length, 

 having the tower of Mount Lheri at one end, and the 

 pyramid of Montmartre at the other extremity of that 

 diftance : their obfervatory was placed between thofe 

 two objects. The refult of their obfervations were 

 thefe, i ft. That found moves one hundred and fe- 

 venty-three fathoms French in a fecond, when the air 

 is calm. ad. That-found moves with the fame degree 

 of fwiftnefs whether it is ftrong or weak ; for thefe 

 gentlemen obferved, that the dilcharge of a box of 

 half a pound of gunpowder exploded at Mont- 

 martre was heard at Mount Lheri in the fame fpace 

 of time as the report of a great gun charged with 

 nearly fix pounds of powder. 3d. That the motion 

 of found is uniform j that its velocity neither acce- 

 lerates nor diminimes through the whole courfe of its 



the ear. The following eafy and common experiment, I think, 

 will prove it. Take any thing whatever, capable of giving a 

 found ; let it be a common poker far inftance, and tying on a 

 garter at top, fo as that both ends of the garter are left at liber- 

 ty; thefe ends muft be rolled round the firfl finger of each hand, 

 and then with thefe fingers flopping the ears clofe, ftrike the poker 

 thus fufpended againft any body whatfoever. The depth of the 

 tone which this new mufical inftrument returns will be amazing. 

 The deepeft and largeft bell will not equal it. Whence is thisv 

 nnlefs from the clofe approach of the founding body, whofe vi- 

 bration* are immediately communicated to the internal parts of 

 the ear. I am fenfible that many objections may be made to tlri 

 laft opinion; fucceeding experience muft, however, determine 

 whether it be juft or not; but fuch as make them muft be particu- 

 larly careful not to let their former experience correct their im- 

 mediate fenfations. This alteration of tone, with diftance, how- 

 ever, muft diminim but by great intervals. GoMfmith's Pbilofopky, 

 vol. u. p. 195, it,6. 



jprogrefs. 



