300 M. Savart on Acoustic Figures produced by Vibration. 



M. Savart next applies these principles to a method of ap- 

 preciating very small quantities of sound. He stretches a 

 piece of thin vegetable paper or goldbeater's skin across the 

 mouth of a glass about four inches in diameter. He then co- 

 vers this with sand, and ascertains the intensity of different 

 sounds by the distance at which they cease to agitate the 

 membrane ; and he remarks that they will often be moved by 

 an augmentation of sound which the ear itself is incapable of 

 appreciating. He proposes also to use it for ascertaining the 

 augmentations of sound which arise from the coincidence of vi- 

 brations produced by numbers of vibrations not very distant 

 from each other. 



Bodies which are neither rigid in themselves, and which are 

 not rendered rigid by tension, such as the skin, a silken fabric, 

 paper, &c. are, even when they are not stretched, susceptible of 

 being thrown into vibrations by the influence of a body vibrating 

 at a distance ; and it appears, that, under some circumstances, 

 they are even more susceptible of this kind of action than 

 most elastic membranes. This may be proved by covering a 

 horizontal portion of any of these substances with sand, and 

 sounding the pipe of an organ at the distance of a foot or so. 

 The sand will be violently agitated, and will form figures 

 composed of numerous curved and bending lines interlaced 

 with one another. 



In the second part of this able memoir, M. Savart applies 

 these experiments to the illustration of the uses of the mem- 

 brane of the tympanum, and of those of the external ear, 

 both of which, as he shows by direct experiments on the ears 

 of animals, are susceptible of being thrown into a state of vi- 

 bration, by bodies vibrating at a distance. As our limits will 

 not permit us to follow our author through his numerous and 

 interesting details, we shall conclude this abstract with an enu- 

 meration of the leading results which he has obtained. 



1. That it is not necessary to suppose, as has hitherto been 

 done, the existence of a particular mechanism, for continually 

 bringing the tympanum to vibrate in unison with the bodies 

 which act upon it. It is evident, that the tympanum is always 

 in a condition to be influenced by any number of vibrations. 



2. That its tension does not probably vary, unless to aug- 



