KEY AND INDEX 



usually by a gasoline engine, but sometimes by steam or by 

 electricity, sprang into popularity in the last decade of the nine- 

 teenth century, but its prototypes (propelled by steam) were 

 made more than a hundred years earlier. See "The Coming of 

 the Automobile," Vol. VII, p. 156. 



Axe. This familiar implement is essentially a sharp wedge 

 operated at the end of a lever. Its use dates from the Rough 

 Stone Age. See "Applications of Muscular Energy," Vol. VI, 

 P- 52- 



Babylonian Medicine. The practice of medicine in Babylonia- 

 Assyria was closely bound up with astrology and magic; yet it 

 had certain more scientific aspects. See "Chaldean Magic," Vol. 

 I. p. 69, and "Babylonian Medicine," Vol. I, p. 75. 



Babylonian Science. The science of the Chaldeans, Babylo- 

 nians, and Assyrians is usually somewhat vaguely included under 

 this title. Our knowledge of the subject depends partly upon 

 Greek traditions (Herodotus, Diodorus), and partly upon re- 

 cently exhumed archaeological remains. See "Science of 

 Babylonia and Assyria," Vol. I, p. 56. 



Bacteria. Microscopic vegetable organisms, which play an 

 all-important part in the economy of nature, causing putrefactive 

 changes, contagious diseases, etc. Discovered by Leeuwenhoek 

 in 1683. Their real importance was unsuspected until late in the 

 nineteenth century. For the importance of the part played by 

 bacteria in surgery, and the discovery of a method of com- 

 batting their effect, see "Lister and Antiseptic Surgery," Vol. 

 IV, p. 229. For recent studies in pathogenic bacteria, see "Some 

 Medical Laboratories and Medical Problems," Vol. V, p. 182. 



Barometer. An instrument for measuring the weight of the 

 atmosphere; in its simplest form, a vacuum tube closed at one 

 end and inverted over a dish of mercury; the height to which 

 the mercury rises in the tube demonstrates the atmospheric 

 pressure, which varies with the altitude and with the amount 

 of moisture in the air. Invented by Torricelli in 1643. See 

 "Torricelli," Vol. II, p. 120; also Pascal's test of the barometer 

 by ascending a mountain and noting the lowering of the column 

 of mercury, see Vol. II, p. 122. 



Bicycle. A familiar two-wheeled vehicle, the most primitive 

 form of which (termed the hobby horse) was introduced by 

 Baron Von Drais in France about the year 1818. The halting 

 stages by which the machine was perfected illustrate the rarity 



[16] 



