6 NATURE AND LIFE. 
sky-blue tint at first seen in the receiver. In this experiment 
Wwe pass in steady progress from the free atom of sulphur 
parted fromthe oxygen-atom by the ether-waves to a mass 
apparent to the senses; but, if this mass is made up of free 
molecules which defy the strongest magnifiers, what must 
be the particles which have produced those very molecules ! 
A last instance of another kind will complete the proof 
as to the minuteness of the elements of matter. When a 
clear solution of sulphate of aluminum is poured into an — 
equally clear solution of sulphate of potassa, the mixture 
at once grows turbid, and after a few seconds myriads of 
little crystals, sparkling like diamonds, make their appear- 
ance in the liquid, which are nothing else than crystals of 
alum. If we suppose the diameter of these crystals to be 
gis of an inch, it will follow from this experiment that in 
the lapse of a few seconds crystals had the power of pro- 
ducing themselves containing tens of millions of molecules, 
each composed of ninety-four atoms, grouped in admirable 
harmony. The motions of these chemical atoms take place 
under the influence of the same forces that guide the 
motions of those enormous agglomerations of atoms called 
stars. The revolution of one sun around another takes a 
thousand years, while these atoms in course of combination 
perform hundreds of millions of such revolutions in the 
millionth part of a second ! 
By varied and delicate calculations, Thomson has suc- 
ceeded in establishing the fact that, in liquids and trans- 
parent or translucent solids, the mean distance between the 
centres of two contiguous atoms is comprised between the 
ten-millionth and the two-hundred-millionth part of > of an 
inch. It is not easy to form an exact conception of dimen- 
sions so small, of which nothing, among the objects that 
affect our senses, can convey any idea. Thomson judges 
that the following comparison may aid us to appreciate 
them: If we imagine a sphere as large as a pea magnified, 
