448 NOTICES OF THE MEETINGS [May 19, 
electric spark ; this method corroborated the result before arrived at 
by Savart, that the lower portion of a liquid vein owes its turbidity 
to the fact of the mass being there reduced to drops, although the 
quickness with which they succeed each other gives the eye the 
impression of continuity. Savart’s Jast experiments on this subject 
were repeated : a tube about five feet long and two inches wide 
had a perforated brass disk fixed at its lower extremity; the tube 
was filled with water, which, after it had become motionless, was 
permitted to issue from an orifice pierced in the centre of the 
disk. As the liquid escaped it gave birth to a succession of mu- 
sical notes of sufficient intensity to be distinctly heard through- 
out the theatre. That these notes were not due to the motion 
imparted to the air by the descending drops of the liquid vein 
was proved, first, by intercepting the vein in its continuous 
portion, and secondly, by permitting it to discharge itself into a 
vessel containing water, the orifice being caused to dip beneath 
the surface of the latter. In this case the mass of liquid was con- 
tinuous, but the notes were nevertheless produced ; thus shewing 
that the vibrations which produce them must take place in the glass 
cylinder itself ;— and corroborating the conclusions arrived at by 
Savart from his earliest experiments on this subject. The pitch 
of the note depends upon the height of the liquid column which 
produces it; and by attaching a tube of an inch in diameter, 
furnished with a perforated bottom, to a cylindrical vessel about 
eighteen inches wide, and filling the whole with water, a note of 
long duration and of sensibly constant pitch was obtained. 
The Lecturer concluded with an experimental illustration of the 
total reflexion of light at the common surface of two media of dif- 
ferent refractive indices. The tube communicating with the 
reservoir before referred to was fitted into the top of a small 
box, into one of the sides of which was fitted a glass tube three 
quarters of an inch wide and five inches long. ‘The side of the 
box opposite to that through which the glass tube was introduced 
was of glass. Behind the box was placed a camera, by means of 
which the electric light could be condensed and caused to pass, first 
through the glass back of the box, and then through the tube in 
front, so as to form a white disk upon a screen held in the direct 
path of the light. When, however, the cock was turned so as to 
permit water to spout from the tube, the light on reaching the 
limiting surface of air and water was totally reflected, and seemed 
to be washed downward by the descending liquid, the latter 
being thereby caused to present a beautiful illuminated appear- 
ance, 
[se 9a 
