This experiment shows that silex possesses some remarkable affinity for the magnetic fluid, since in this case it had robbed the steel of it, for those spherules would not answer to the magnet. May not, therefore, the rows of flints in the cliff have attracted the lightning in severe thunderstorms, and been shivered by the blow? This would not necessarily hurl the chalk down. * * * * * The Arabs have a proverb which says, “Under the lamp it is dark.” Certainly, the chief mystery of every animated creature seems to reside _in its life_, and _Life_ is like a burning lamp. Once the life extinct, we can anatomize and analyze, and arrive at many partial conclusions; but, meanwhile, the life has departed, and we do not know what that was. The nearest thing to its likeness is _expression_; and animals rank high in the scale of being, according as they command and impart expression. A dog or horse have a great deal; a bird some; a reptile or insect, absolutely none to our eyes. With these latter, however, their _habits_, while alive, take the place of any more intelligent expression; especially some of their more excited movements. We know by the _sound_, when a snake is angry; and as to motion, the attack of a provoked hornet is a startling thing to witness. Ordinarily speaking, however, all their habits tend to concealment; no doubt, for the sake of safety. I believe no one ever sees the Sphynx-moth, called a “Death’s-head” (_Acherontia Atropos_), on the wing. Yet we discern many others which, like it, fly in the hours of dusk. But this insect whirls through the air like a stone from a sling. It has never yet, in my experience as a naturalist, been my lot to meet with the burrowing insect called an Ant-lion. Only twice in my life have I encountered a slow-worm in the woods of Devon and the Isle of Wight. And to instance the case of a far commoner creature, how seldom does it happen to any one to take the large dragon-fly behind his green leaf! * * * * * And yet the problems of inanimate matter are perhaps the most difficult to solve. They have deeply exercised philosophers in every age of the world.