Springs, in various parts of this and other countries, alternately ebbing and flowing, have been, and are still, in some cases, supposed to be under the ban of witchcraft. And yet the phenomena are easily explained by natural laws. If the shorter end of a bent tube, A, whose branches are of an unequal length, be placed in a basin of water, and the air is drawn from it, we have a syphon, which will decant the water into any vessel. Now such tubes as these are naturally formed in the earth, and if the water be drained into a cavity, B, having a syphon-like channel, C, it is evident that it will flow as long as the syphon can act, and it will then cease. [Illustration] Seneca describes a spring near to Tempe, in Thessaly, the waters of which are fatal to animals, and penetrate iron and copper. Yet, it is probable, as Dr. Thomson states, that “this spring contained either free sulphuric acid, or a highly acidulous salt of that acid. This acid has been detected in a free state, as well as hydrochloric acid, in the water of the Rio Vindagre, which descends from the volcano of Paraiè, in Columbia, South America. Sulphuric acid is also found in the waters of other volcanic regions. The sour springs of Byron, in the Genessee country, about sixty miles south of the Erie canal, contain sulphuric acid. Such waters would rapidly corrode both iron and copper, converting the former into green, the latter into blue vitriol--sulphates of both metals.”[E] It would be easy to extend these instances, in connexion with the phenomena of the globe, but the present will suffice to show that a little knowledge of natural science is an antidote to many superstitions. We proceed now to illustrations of agencies in active operation of a different character. CHAPTER V. Chemical wonders--Ice obtained in a red-hot vessel--The corpse candles of Wales--Luminous appearances after death--Sadoomeh the magician--The laughing gas--Sulphuric ether--Chloroform--Gunpowder compared with gun-cotton. The word chemistry is, probably, derived from a Coptic root, signifying obscure or secret; and the German word _geheim_ is traced to the same origin. The objects of this department of science are, to investigate the nature and properties of the elements of matter and their mutual actions and combinations; to ascertain the proportions in which they unite and the modes of separating them when united; and to inquire into the laws which affect and rule these agencies. A few of the wonders connected with this science may, therefore, appropriately follow the terrestrial phenomena which have just been considered.