Apparatus to illustrate Work by Diffusion. 
375 
reasons, unless it mean that measurables do, as a matter of 
fact, as often have one value as another. But, in touching 
these considerations, we have already passed the frontier which 
separates mathematical reasoning from general philosophy. 
It remains only to add that the preceding problems are im- 
mensely complicated when, instead of our single variable x, 
there are several variables; but that these additional difficulties 
have been triumphed over by a long line of distinguished 
mathematicians, from Laplace to Glaisher. 
LI. Description of an Apparatus to illustrate the Production 
of Work by Diffusion. By C. J. Woodwaed, B.Sc* 
DIFFUSION, as a source of energy, is usually shown in 
the lecture-room by bringing a jar of hydrogen over a 
porous vessel fitted up with a glass tube dipping into water. 
Hydrogen, by inward diffusion, enters the jar; the internal 
pressure thus produced forces the water down, and a stream of 
bubbles escapes from the tube. On removing now the jar of 
hydrogen, outward diffusion of the hydrogen takes place, a 
minus pressure is produced in the porous vessel, and the water 
is lifted. 
The apparatus I am about to describe is an adaptation of this 
experiment to the production of an oscillatory movement of a 
beam from alternate inward and outward diffusion of hydrogen. 
-*% 
The apparatus is represented in the annexed figure. A A 
is a scale-beam about 3 feet long, carrying at one end a scale- 
* Communicated by the Physical Society, having been read at 'the 
Meeting on May 12th, 18S3. 
