ES eee eg et ae I ene a 
John LeConte—Sound-Shadows in Water. 29 
5. The mathematical theory of undulations indicates that 
cast by acute sounds were more distinct than those produced by 
grave sounds. 
large, and the sounds must be acute. Lord Rayleigh has re- 
cently succeeded in experimentally verifying this prevision of 
theory in the case of sound, by means of a circular disk about 
fifteen inches in diameter, with a bird-call as the source of 
sound, placed at a distance of twenty inches from the center of 
the plane of the disk. At twenty-four inches on the farther 
side of the disk, the augmentation of the intensity of the sound, 
in the axis of the acoustical shadow, was obvious both to the 
ear and to a sensitive flame.t+ 
Sounb-SHADOWS IN WATER. 
It is a significant fact in relation to the phenomenon of 
acoustical shadows, that they seem to be more perfect or more 
sharply defined in water than in air. Thus, during the progress 
of the classical experiments of Daniel Colladon, in November, 
1826, on the velocity of sound in the waters of the lake of Ge- 
neva, this physicist incidentally observed, that when the end 
of the hearing-tube (cornet acoustique), plunged into the water, 
was screened from rectilinear communication with the bell by 
* Phil. Mag., 5th series, vol. iii, pp. 458, 459, 1877. 
+ Phil. Mag., 5th series, vol. ix, pp. 281, 282, 1880. 
