Now, this exactly corresponds with what we have seen of the form of the crystal, and shows that the polar arrangement of the molecules producing different shapes at the two ends, also produces corresponding electrical properties. Crystal form, heat, electricity, and even light, are therefore seen to have intimate connection, and it may be that this interesting mineral will furnish us a means of learning more about these forces. In composition Tourmaline is a complex silicate chiefly of aluminum and boron. Iron, magnesium, the alkalies, and water also enter in varying amounts into it. In fact, so complicated is its chemical nature that perhaps no other mineral has been so often analyzed or had its analyses so much discussed. Ruskin, in his “Ethics of the Dust,” thus describes its composition: “A little of everything; there’s always flint and clay and magnesia in it; and the black is iron according to its fancy; and there’s boracic acid, if you know what that is, and if you don’t, I cannot tell you to-day, and it doesn’t signify; and there’s potash and soda, and, on the whole, the chemistry of it is more like a mediæval doctor’s prescription than the making of a respectable mineral.” As to its hardness and specific gravity, Tourmaline may be said to be both harder and heavier than quartz, its hardness being 7-7.5 in the scale of hardness of which the diamond is 10. Its specific gravity is 2.98-3.20. These qualities fit it admirably for use as a gem. It is, however, quite brittle and even at times friable. Cracks therefore frequently cut across good crystals and spoil what would otherwise make a good gem. It is very common to find tourmalines in the rocks broken into a number of pieces and the fragments “mended” together with quartz or calcite. This has been true of the black Tourmaline shown in the accompanying plate. Scarcely any other mineral exhibits this change so often as Tourmaline, a result due probably to its brittleness and the character of the rock in which it occurs. I have shown how one of the most remarkable properties of Tourmaline was discovered by children. It is also interesting to know that the locality of the finest Tourmalines in the world was discovered by two boys named Elijah L. Hamlin and Ezekiel Holmes. They were interested in the study of minerals and spent much of their leisure time searching for them. One day in the fall, having been out many hours hunting for new minerals, they were about to return home when a gleam of something green at the roots of a tree caught their eye. Eagerly bringing it to light, they found it to be a beautiful green Tourmaline. A fall of snow that night prevented their obtaining more of the crystals, but the following spring they returned and secured many fine gems. For many years thereafter the locality furnished gems of purest ray serene which have gone to adorn the coronets of kings and enriched the mineral cabinets of the world.