Who would suppose, for instance, that water--which every body knows, extinguishes fire--may, under certain circumstances, add fuel to flame, so that the "coming man," who is to "set the Thames on fire," may not be far off. If we take some mystical gray-looking globules of potassium (which is the metallic basis of common pearl-ash) and lay them upon water, the water will instantly appear to ignite. The globules will swim about in flames, reminding us of the "death-fires" described by the Ancient Mariner, burning "like witches' oil" on the surface of the stagnant sea. Sometimes even, without any chemical ingredient being added, fire will appear to spring spontaneously from water; which is not a simple element, as Thales imagined, when he speculated upon the origin of the Creation, but two invisible gases--oxygen and hydrogen, chemically combined. During the electrical changes of the atmosphere in a thunder-storm, these gases frequently combine with explosive violence, and it is this combination which takes place when "the big rain comes dancing to the earth." These fire-and-water phenomena are thus accounted for; certain substances have peculiar affinities or attractions for one another; the potassium has so inordinate a desire for oxygen, that the moment it touches, it decomposes the water, abstracts all the oxygen, and sets free the hydrogen or inflammable gas. The potassium, when combined with the oxygen, forms that corrosive substance known as caustic potash, and the heat, disengaged during this process, ignites the hydrogen. Here the mystery ends; and the contradictions are solved; Oxygen and hydrogen when combined, become water; when separated the hydrogen gas burns with a pale, lambent flame. Many of Nature's most delicate deceptions are accounted for by a knowledge of these laws.