M. Savart on the Influence of' different Media, «J-c. 49 



sively in media of different, densities, but hitherto all these at- 

 tempts have been fruitless. This has arisen not only from 

 our wanting a suitable method of causing bodies to vibrate in 

 media of different kinds, but also from our not having acquir- 

 ed correct notions of the modes of vibrations of the bodies 

 themselves ; — for the action of the same medium on the num- 

 ber of vibrations of a body is different, according as the body 

 is the seat of tangential longitudinal vibrations, — tangential 

 transverse ones, or normal ones more or less oblique. 



This action is nothing for very long and very thin bodies, 

 which execute vibrations in the direction of their length, at least 

 it seems to be so, if we judge by the impression produced on 

 the organ of hearing ; for a rod very long, and of a small dia- 

 meter, affected with this kind of motion, appears to emit ex- 

 actly the same sound in media of very different densities, such 

 as air, water, acids, oil, and even mercury. 



On the contrary, in the same circumstances, bodies which 

 execute normal vibrations emit sounds which may differ much 

 from one another. It may happen, for example, that the 

 sound of a thin plate, which resounds in air, may become 

 more grave by a third, a fifth, an octave, two octaves, &c. 

 when it resounds in water, or in other liquids, either of greater 

 or lesser density. We cannot determine any thing respecting 

 this descent of the sound, because it depends on the relations 

 between the dimensions of the plate. If its width and length 

 become considerable at the same time that its thickness is 

 smaller, the more will the number of its vibrations diminish by 

 immersion in a denser fluid, such as water, for example. In 

 order to verify this result, we must be able to impress upon 

 a body normal vibrations, by a method which may be employ- 

 ed indifferently in all media. This may be easily done by ex- 

 citing the motion with a small glass tube, which is rubbed 

 lightly in the direction of its length, and which is fixed per- 

 pendicularly on one of the faces of a body which it is wished 

 to make vibrate. 



When the bodies execute tangential transverse vibrations, 

 a kind of motion which we may produce by the method which 

 we have pointed out for normal vibrations, the alterations 

 produced in the number of vibrations by media of greater 



VOL. v. NO. I. JULY 1826. D 



