6 NATURE AND LIFE. 



sky-blue tint at first seen in the receiver. In this experiment 

 we pass in steady progress from the free atom of sulphur 

 parted from the 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 

 -% 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 1 



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 -fa 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, 



