328 



THE CENTURY BOOK OF FACTS. 



has occupy parts of the Soudan ; the former, 

 in the N. W., extend from the Senegal and 

 Niger towards Lake Tchad ; the latter are 

 found in Nubia, Kordofan, Darfur, etc. The 

 Gallas, Copts, Somali, of the Sahara, Egypt, 

 and East Africa ; the Abyssinians ; and the 

 Berbers, Kabyles, Tuareks and other tribes of 

 North Africa, belong to the Hamitic race, 

 which is closely allied to the Semitic race. 

 The latter is represented by the Arabs of the 

 N. coast, and of the Arabian Peninsula, and 

 by the Tigres and other tribes of Abyssinia. 



Hypnotism is a method for the alleged 

 cure of disease, by the concentrated action of 

 the mind upon the body while in a state of 

 trance, induced by causing the patient to fix 

 his eyes and concentrate his mind upon a disc 

 of bright metal held at a distance of about 

 twelve inches above the level of the eyes. 

 The first effort to investigate hypnotism in a 

 scientific manner was made by James Braid, 

 of Manchester (1846), from which circum- 

 stance hypnotism is sometimes called Braidism. 

 The power to hypnotize is possessed only by per- 

 sons of peculiar mental organization. While 

 in the hypnotized condition, which renders 

 them insensible to pain, patients may be op- 

 erated upon for surgical or medical purposes, 

 the patient being entirely subject to the will of 

 the hypnotizer. Hypnotism can, however, only 

 be considered as of quasi medical utility, 

 though investigation is being made with the 

 view to placing it on a sound scientific basis. 



Igneous Rocks are those which have 

 been produced from materials fused by heat. 

 They differ from the sedimentary rocks in 

 their origin, structure, and position. They 

 invariably come from below upward, breaking 

 through the older rocks, and are generally 

 ejected in a melted state from volcanic vents, 

 or from fissures opened to some seat of fires 

 within or below the earth's crust. The mate- 

 rials of sedimentary strata are fragments of 

 pre-existing rocks worn by the action of water 

 either into a fine mud or into rounded particles 

 of greater or less size ; whereas igneous rocks 

 exhibit either a vitreous structure, as when 

 they have, been quickly cooled, or a granular 

 structure composed of more or less minute 

 crystals, according to the rate of cooling, or a 

 vesicular structure when they have been ex- 

 panded by the contained gases, or by being 

 brought into contact with water. In position, 

 also, they may be distinguished from the sedi- 

 mentary rocks, very seldom occurring regularly 

 stratified with parallel upper and under sur- 

 faces, but generally local, thinning out into 

 wedge-shaped beds, or having that irregular 

 stratification which may be seen in modern 

 lava. They are also found as upright walls 



and columns, of which the famous Giant's 

 Causeway and Fingal's Cave are notable ex- 

 amples. Igneous rocks when filling a narrow 

 fissure in an older stratum, and also when 

 speading beyond the fissure and forming an 

 extensive superstratum, are called a dike. The 

 rocks above mentioned are dikes, as are also 

 the Palisades on the Hudson, Salisbury Cra^ 

 near Edinburgh, many rocks around Lake Su- 

 perior, over the western slope of the Rocky 

 Mountains, and numerous other localities. 

 The outflow in some cases has been very large, 

 the lava floods of Oregon, Nevada, and north- 

 ern California being estimated to comprise a 

 total area of not less than 200,000 square 

 miles, with a maximum thickness of 3,500 

 feet, the average being probably 2,000 feet. 

 The most common rocks of dikes are dolerite 

 (often called trap) and peridotite ; both some- 

 times called basalt when not granular in text- 

 ure. 



Ignis-Fatuus. A number of theories 

 have been advanced in explanation of the lu- 

 minous appearance which is frequently seen in 

 marshy places, church yards, and stagnant 

 pools, and which is known as ignis-fatuus. 

 Of these it is only necessary to mention two. 

 The first is that the ignis-fatuus is due to phos- 

 phureted hydrogen gas, which possesses the 

 power of spontaneous ignition on coming in 

 contact with dry atmospheric air ; the gas 

 would be generated by the decomposition of 

 animal matter present in a marshy soil. The 

 motion of the ignis-fatuus (it floats in the air at 

 about two feet from the ground, is sometimes 

 fixed, and sometimes travels with great rapid- 

 ity) is accounted for by the flame being com- 

 municated along the line of a stream of gas. 

 The second is that it is due to the combustion of 

 light carbureted hydrogen gas arising from the 

 decomposition of vegetable matter ; but, though 

 this supposition satisfactorily accounts for 

 many appearances connected with the ignis- 

 fatuus, the gas itself is not spontaneously com- 

 bustible, and an additional supposition re- 

 quires to be made to account for its ignition. 

 The ignis-fatuus generally appears a little af- 

 ter sunset as a pale, bluish-colored flame, vary- 

 ing in size and shape; sometimes it shines 

 steadily till morning, at other times disappears 

 and reappears within about half -hourly inter- 

 vals. In general it recedes on being ap- 

 proached, and rice versa, though several suc- 

 cessful attempts have been made to light a 

 piece of paper by it. In former times, under 

 the names ofWill-o'-the-Wi*/>, Jack-o'-Lantenti 

 S/>/nikie, etc., it was an object of superstition 

 among the inhabitants of the districts where it 

 appears, and w r as believed to be due to the 

 agency of evil spirits attempting to lure the 





