and also free from all danger.  I kindle a vivid flame of an intensely yellow color, which I think the ladies will unanimously agree is not at all becoming to their complexions, while the pretty dresses have lost their variety of colors.  Here is a nice bouquet, and yet you can hardly distinguish the green of the leaves from the brilliant colors of the flowers, except by trifling differences of shade.  Expose to this light a number of pieces of variously colored ribbon, pink and red and green and blue, and their beauty is gone; and yet we are told that this yellow is a perfectly pure color; in fact, the purest color that can be produced.  I think we have to be thankful that the light which our good sun sends us does not possess purity of that description.  There is one substance which will produce that yellow light; it is a curious metal called sodium—­a metal so soft that you can cut it with a knife, and so light that it will float on water; while, still more strange, it actually takes fire the moment it is dropped on the water.  It is only in a chemical laboratory that you will be likely to meet with the actual metallic sodium, yet in other forms the substance is one of the most abundant in nature.  Indeed, common salt is nothing but sodium closely united with a most poisonous gas, a few respirations of which would kill you.  But this strange metal and this noxious gas, when united, become simply the salt for our eggs at breakfast.  This pure yellow light, wherever it is seen, either in the flame of spirits of wine mixed with salt or in that great blaze at which we have been looking, is characteristic of sodium.  Wherever you see that particular kind of light, you know that sodium must have been present in the body from which it came.

We have accordingly learned to recognize two substances, namely, strontium and sodium, by the different lights which they give out when burning.  To these two metals we may add a third.  Here is a strip of white metallic ribbon.  It is called magnesium.  It seems like a bit of tin at the first glance, but indeed it is a very different substance from tin; for, look, when I hold it in the spirit-lamp, the strip of metal immediately takes fire, and burns with a white light so dazzling that it pales the gas-flames to insignificance.  There is no other substance which will, when kindled, give that particular kind of light which we see from magnesium.  I can recommend this little experiment as quite suitable for trying at home; you can buy a bit of magnesium ribbon for a trifle at the opticians; it cannot explode or do any harm, nor will you get into any trouble with the authorities provided you hold it when burning over a tray or a newspaper, so as to prevent the white ashes from falling on the carpet.