164 MR GOODCHILD. 
ensues some little preliminary explanation is needed :— 
Surface Energy operates proportionately to the area of the 
surface exposed; where that area is small, the effect pro- 
duced is small also; where the area is large, there also is 
the result. To explain this more fully we need only refer 
to the quantity, say, of soap solution that a ball of worsted 
would take up and hold to itself, as compared with what a 
solid ball of the same dimensions would do. In the case of 
the ball of worsted, especially if loosely rolled, the quantity 
of fluid taken in and held may be twenty times as great as 
what a solid ball would hold. The volume of both is alike, 
but the surface area presented by the ball of worsted is 
obviously very much greater than that of the solid of the 
same volume. The total surface area presented by the leaves 
of a cabbage, for example, may well be a hundred times that 
of a box in which that cabbage could easily be packed with- 
out any squeezing. Furthermore, Surface Energy always 
tends toa minimum. Hence, as the form of surface which 
is the least in proportion to the volume is that of a sphere, 
it follows that fluids, when their molecules are free to move 
amongst themselves, always tend to assume the spherical form. 
Putting that statement into another form in order to make its 
bearing upon the present question somewhat clearer :—If we 
take a small tuft, say of worsted, and dip it in a solution of 
soap, the first layer of the solution will endeavour to fill up the 
interspaces between the several fibres, and the outer layers 
will tend more and more to level up the irregularities of the 
surface, so as to convert the whole into a nearly spherical 
drop. If we could manage to consolidate many such drops, 
and were then to bring some of them together and get them 
to take up still more of the soap solution, each two con- 
tiguous beads would tend to unite into one with an ellipsoid 
shape, and, if we continued the process, the whole bundle 
would gradually enlarge from the ellipsoid in such a manner 
as to build up a sphere of larger size still. 
This is very much what happens with the tufts of zeolites. 
Each chalcedonic coating tends to form a bead around the 
tuft ; and the successive layers of which the bead is formed 
may consist of Chalcedony of various shades of colour or 
of translucency. If we were to take one of these beads, 
