i88oJ 
On Water and Air 
515 
Cartesian Diver. The diver (Fig. 38) consists of a glass 
figure having attached to its head a hollow ball. The figure 
and ball are entirely closed, except a small opening in the 
curled tail, D, which is affixed to the body of the figure. A 
quantity of water has been introduced into the figure and 
ball, so that at the present time it is slightly lighter than 
the water in which it is contained. In the jar, ab, the 
proportions between the air and the water are such that the 
diver floats ; but if I press upon this sheet india-rubber 
with which the top of the jar is closed, what do I do ? I 
squeeze the air at the top of the water, there being a little 
air underneath this piece of india-rubber. The compression 
of the air is transmitted to the water; and this is the point 
that I want to make clear to you. The water has the power 
of transmitting the pressure from the air above it, and that 
pressure is transmitted to the little diver below. What is 
the effedt ? It is that the pressure squeezes a certain 
amount of water into the diver, and the consequence is that 
the air within the hollow ball is compressed, and is replaced 
Fig. 38, 
