par as Marig striking manner, and when properly fused and a lidel self-built mystals of great size and beauty are formed of this metal.

47. If you diss Ire saltperre in water, and allow the solution to evaporate slowly, you may obtain large crystals, for no portion of the sult is converted into vapour. The water of our atmosphere is fresh though it is derival from the salt sea. Sagar dissolved in water, and permitted to emaporate, pills crystals of sugarcandy. Alım readily crystallizes in the same way. F....ta d ́escirel, as they sometimes are in nature, and permitted to crystallize, yield the prisms and pyramids of rock opstal. Chalk dissolved and crystallized yields Iceland spar. The Himoniis crystallized carbon. All cur precious stones, the mily, sapphire, beryl, topaz, emeral 1, are all examples of this crystallizing power.

SS. You have heard of the force of gravitation, and you know that it consists of an attraction of every particle of matter for every other partiele. You know that planets and moons are held in their orbits by this attraction. Bat gravitation is a very simple affair compared to the force, or rather forces, of crystallization. For here the ultimate particles of matter, inconceivably small as they are, show themselves possessed of attractive and repellent poles, by the mutual action of which the shape and structure of the crystal are determined. In the solid condition the attracting poles are rigidly locked together; but if sufficient heat be applied the

bond of union is dissolved, and in the state of fusion the poles are pushed so far asunder as to be practically out of each other's range. The natural tendency of the molecules to build themselves together is thus neutralized.

89. This is the case with water, which as a liquid is to all appearance formless. When sufficiently cooled the molecules are brought within the play of the crystallizing force, and they then arrange themselves in forms of indescribable beauty. When snow is produced in calm air, the icy particles build themselves into beautiful stellar shapes, each star possessing six rays. There is no deviation from this type, though in other respects the appearances of the snow-stars are infinitely various. In the polar regions these exquisite forms were observed by Dr. Scoresby, who gave numerous drawings of them. I have observed them in mid-winter filling the air, and loading the slopes of the Alps. But in England they are also to be seen, and no words of mine could convey so vivid an impression of their beauty as the annexed drawings of a few of them, executed at Greenwich by Mr. Glaisher.

90. It is worth pausing to think what wonderful work is going on in the atmosphere during the formation and descent of every snow-shower: what building power is brought into play! and how imperfect seem the productions of human minds and hands when compared with those formed by the blind forces of nature!

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98 • What JM I Tell Than & immens ago (99), I spoke of astmacting and selim ples? Let My try to answve this questiD. To buy that astroHomers and geographers speak of the earth's poles, and you have also heard of magnetic poles, the poles of a magnet being the points at which the attraction and tepulsion of the magnet are as it were concentrated.

PT. Every magnet possesses two such poles; and if

iron filings be scattered over a magnet, each particle becomes also endowed with two poles. Suppose such particles devoid of weight and floating in our atmosphere, what must occur when they come near each other? Manifestly the repellent poles will retreat from each other, while the attractive poles will approach and finally lock themselves together. And supposing the particles, instead of a single pair, to possess several pairs of poles arranged at definite points over their surfaces; you can then picture them, in obedience to their mutual attractions and repulsions, building themselves together to form masses of definite shape and structure.

95. Imagine the molecules of water in calm cold air to be gifted with poles of this description, which compel the particles to lay themselves together in a definite order, and you have before your mind's eye the unseen architecture which finally produces the visible and beautiful crystals of the snow. Thus our first notions and conceptions of poles are obtained from the sight of our eyes in looking at the effects of magnetism; and we then transfer these notions and conceptions to particles which no eye has ever seen. The power by which we thus picture to ourselves effects beyond the range of the senses is what philosophers call the Imagination, and in the effort of the mind to seize upon the unseen architecture of crystals, we have an example of the 'scientific use' of this faculty. Without imagination we might have critical power, but not creative power in science.