Experiments on the Tvanfmifflon of Sound. 41 p 



found, or at lead to produce very little effe£t on thefe fonorous bodies. On thefe confi- 

 derations I made the following experiments : 



Experiment I. I applied the tuning-fork upon a table of wood, and when it had ceafcd 

 to vibrate I applied my watch to the fame furface. The found in each was iiicreafed in pro- 

 portion to their refpedive intenfities. I then removed the wooden top of the table, and 

 fubftituted in its place another of marble, of the fame dimenfions. The tuning-fork and 

 watch were applied as before. The found of the former was augmented, though much lefs 

 than when it was applied on the wooden covering. The found of the watch was fcnrce 

 perceptibly increafed. I could perceive little difference between its found, whether it 

 touched the marble or hung in the air at the fame diftance from the ear. 



Though this experiment flrongly confirms my conjedure, I determined, neverthelefs, 

 to fubjedl it to another proof : 



Experiment II. I placed my watch on the wooden table, and clofed my ears with 

 chewed paper. When the ear was at a few lines diftance from the table, I could not hear 

 the vibrations of the watch. I then placed my ear in contaft with one of the fmall wooden 

 cylinders ufed in the experiments already defcribed. The oppofite end of the cylinder was 

 placed in contaft with the table. 



The found of the watch immediately and forcibly ftruck the ear. I made this application ■ 

 to every part of the table, not excepting even the feet ; and the found was in every cafe dif- 

 tiniStly heard. The experiment was then repeated with the marble covering inftead of the 

 wood. The vibrations of the watch were heard in an imperfetl or indiftinft manner, and 

 only when the wooden cylinder was applied at a (hort dirtance from the fonorous body. 

 I did n,ot ufe the tuning-fork in this experiment, becaufe, in fpite of every precaution, 

 it was not poflible to clofe the ears fo perftdly but that the found fliU remained per- 

 ceptible. 



In order to eftiablifti my conje£lure on the mod folid bafis, it remained to repeat the ex- 

 periments upon tables of all the fubftances ufed in the experiments related in the firft part 

 of this memoir, and to (hew that the refonances follow the proportion of the conducing 

 powers of the bodies. But the difficulties which oppofed the execution of this plan in- 

 duced me to confine my ertquiries to afccrtain whether the refonance does not vary in dif- 

 ferent bodies, as well as the power of tranfraitting found. 



Experiment III. I therefore placed the tuning-fork fucceffwely upon plates of earthen- 

 ware, of porcelain, on plates of glafs, and upon thin ifolated plates of copper and tinned iron. 

 The found was fortified by thefe bodies, and the tone never appeared to be exatlly the fame 

 in any two experiments. 



Thefe tri.ils naturally led me to examine the fame founds upon mufical inftruments. 

 With this view I applied firft the tuning-fork and afterwards the watch, upon bafes, violins, 

 mandolins, guitars, harpfichords, and horns. Both founds were proportionally increafed. 



They appeared to acquire more force and melody by means of the mufical. inftruments 

 tlian on the other bodies. The intenfity fecmed dircftly in proportion to the volume of the 

 inftrument. 



From thefe experiments it follows: — i. That all the fubftances which were tried, which 

 poftcflTcd extended furfaces, fortify the weak founds produced by bodies which touch them, 

 and modify the tone in a manner peculiar to eath. 



2. That 



