The name Ignis Fatuus, or False Fire, is applied to a flickering, bluish light, which is often seen in marshy districts, and in damp burial grounds, either on the surface of the earth or only a small distance above it. So you see it is not strictly a wonder of the sky; but I introduce it here because it seems to be somewhat similar to some of the higher meteors, in the manner in which it is occasioned. A great many entertaining stories are told of persons having mistaken these Ignes Fatui for real lights, and it is said that benighted travellers have frequently been led far astray by them. They are vulgarly called in various parts of the country, Will-o'-the-Whisp, Jack-o'-the-Lantern, Peg with her Lantern, and in burying grounds in Scotland, Grave Candles; and strange superstitious notions are annexed to them. They keep constantly in motion; now rising a few feet above the earth, now sinking to the surface; now seeming to be close to you, disappearing in an instant, and shining out at some distance; at times one of them dividing into two, or two seeming to join into one. I will presently tell you how you can try a simple experiment, that will go a great way towards accounting for these idle Will-o'-the-Whisps. The inflammable gas called Hydrogen, is copiously produced by the decomposition of animal and vegetable bodies. The substance called Phosphorus, is contained in animal bodies, and is set at liberty in small quantities by their decomposition. When phosphorus and hydrogen come together under certain circumstances, they mix, and a gas called Phosphuretted Hydrogen is the result. There is, therefore, no difficulty in supposing that most marshy grounds may produce this gas; and this experiment will show that it is very likely that the Will-o'-the-Whisp is nothing more. Hydrogen may be obtained by pouring diluted Sulphuric acid on small pieces of Iron or Zinc. If you mix very small pieces of Phosphorus with very small pieces of Zinc, and put them into a glass, and pour over them the acid, Phosphuretted Hydrogen will be sent off, and the surface of the acid will be covered with a beautiful blue flame of the very colour of the Ignis Fatuus. The cause of the flame is, that the phosphuretted hydrogen is so wonderfully inflammable, that the moment it comes into air of a common temperature, it bursts into flame. If you try this experiment, you will see how likely it is that the Will-o'-the-Whisp is an escape of this gas from the surface of the earth. CHAPTER IV. SHOOTING STARS.