L. I do not know.  Miss Mary; I do not even know if anybody knows.  The smallest atoms which are visibly and practically put together to make large crystals, may better be described as “limited in fixed directions” than as “of fixed forms.”  But I can tell you nothing clear about ultimate atoms:  you will find the idea of little bricks, or, perhaps, of little spheres, available for all the uses you will have to put it to.

Mary.  Well, it’s very provoking; one seems always to be stopped just when one is coming to the very thing one wants to know.

L. No, Mary, for we should not wish to know anything but what is easily and assuredly knowable.  There’s no end to it.  If I could show you, or myself, a group of ultimate atoms, quite clearly, in this magnifying glass, we should both be presently vexed, because we could not break them in two pieces, and see their insides.

Mary.  Well then, next, what do you mean by the flying of the bricks?  What is it the atoms do, that is like flying?

L. When they are dissolved, or uncrystallized, they are really separated from each other, like a swarm of gnats in the air, or like a shoal of fish in the sea;—­generally at about equal distances.  In currents of solutions, or at different depths of them, one part may be more full of the dissolved atoms than another; but on the whole, you may think of them as equidistant, like the spots in the print of your gown.  If they are separated by force of heat only, the substance is said to be melted; if they are separated by any other substance, as particles of sugar by water, they are said to be “dissolved.”  Note this distinction carefully, all of you.

Dora.  I will be very particular.  When next you tell me there isn’t sugar enough in your tea, I will say, “It is not yet dissolved, sir.”

L. I tell you what shall be dissolved, Miss Dora; and that’s the present parliament, if the members get too saucy.

(Dora folds her hands and casts down her eyes.)

L. (proceeds in state).  Now, Miss Mary, you know already, I believe, that nearly everything will melt, under a sufficient heat, like wax.  Limestone melts (under pressure); sand melts; granite melts; the lava of a volcano is a mixed mass of many kinds of rocks, melted:  and any melted substance nearly always, if not always, crystallizes as it cools; the more slowly the more perfectly.  Water melts at what we call the freezing, but might just as wisely, though not as conveniently, call the melting, point; and radiates as it cools into the most beautiful of all known crystals.  Glass melts at a greater heat, and will crystallize, if you let it cool slowly enough, in stars, much like snow.  Gold needs more heat to melt it, but crystallizes also exquisitely, as I will presently show you.  Arsenic and sulphur crystallize from their vapors.  Now in any of these cases, either of melted, dissolved, or vaporous bodies, the particles are usually separated from each other, either by heat, or by an intermediate substance; and in crystallizing they are both brought nearer to each other, and packed, so as to fit as closely as possible:  the essential part of the business being not the bringing together, but the packing.  Who packed your trunk for you, last holidays, Isabel?