8 



EXPLANATION OF SCIENTIFIC TERMS. 



circles cut the horizon at right angles ; 

 and it is in an arc of one which passes 

 through a star that the altitude of the 

 star above the horizon is measured. The 

 vertical circle which passes through the 

 place of the sun at noon, cuts the horizon 

 at the north and south points, and is called 

 the meridian of the place where it is 

 supposed to be drawn. Any other vertical 

 plane which may be imagined to pass 

 through the sun, or a star, when not in 

 the meridian, will make an angle with 

 the plane of the meridian, which will he 

 measured by the portion of the circle of 

 the horizon which it cuts off to the east 

 or west of that meridian. This angle, or 

 portion of the circle of the horizon is called 

 the Azimuth of the sun, or star, at that 

 time and place. The Magnetic Meridian, 

 as pointed out by the Mariner's Compass, 

 differs from the true (or real north and 

 south) by the amount of the Variation of 

 the Compass, and so does the apparent or 

 Mctgneiical Azimuth. The Azimuth Com- 

 pass is constructed so as to find easily 

 the magnetical azimuth. See Magnetism, 

 pages 60, 68 72- An arch, intercepted 

 between the east or west point of the 

 horizon, and the point (of the same circle) 

 of the rising or setting of the sun or of a 

 star, on any particular day, is called the 

 Amplitude of the sun, or star, for that 

 day. The distances of the points of 

 rising or setting from the east and west, 

 as shown by the compass, is the Magneti- 

 cal Amplitude. 



HYACINTH. See Zircon. 



HYDRATES. Chemical compounds, par- 

 ticularly salts, which contain water as 

 one of their ingredients, have been termed 

 Hydrates. If water is not a constituent, 

 they are said to be Anhydrous : a Greek 

 compound which signifies without water. 



HYDROUS, watery, or containing water 

 in its composition. 



HYDROGEN. See Oxygen. 



HYGROMETER, an instrument, of which 

 there are various forms of construc- 

 tion, for measuring the relative degree 

 of moisture which exists, at any par- 

 ticular time and place, in the atmos- 

 phere. 



HYPERBOLA. See Cone, and Conic Sec- 

 tions. 



HYPERBOLOID. See Conoid. 



HYPOTHESIS. See Induction. 



ICELAND SPAR. See Calcareous Spar, 

 and Spar. 



ICOSAHEDRON. See Rhombus. 



IDOCRASE, a name sometimes given to 

 Fesnvian, which see. 



IMPENETRABILITY. See Gloss. I. 



IMPULSE. See Gloss. I. 



INCIDENCE, POINT OF. See Gloss. I. 



INCOMMENSURABLE. -See Ratio. 



INSTRUMENT. See Machine. 



INDEX OF REFRACTION. See Re- 

 fracttve power. 



INDIAN RUBBER. See Caoutchouc. 



INDUCTION, in philosophy, is the col- 

 lecting, or bringing into one focus, a mul- 

 titude of observations on any particular 

 subject, and drawing conclusions from 

 an examination and general survey of 

 the whole. It is the opposite of Hypo- 

 thesis, which is to lay down a theory in 

 the outset, and trusting to future experi- 

 ments, or example, for its proof. 



IN ELECTRICITY is that 



effect of an insulated electrified body which 

 tends to produce an opposite electric state 

 in neighbouring bodies. 



IN MAGNETISM is analo- 

 gous to electric induction ; for illustra- 

 tions of which see Magnetism, page 4. 



INERTIA. See Ks Inertia. 



INFLAMMABLE AIR. See Oxygen. 



INFLEXION OF LIGHT. See Diffrac- 

 tion. 



INSULATION. See Gloss. I. 



INVERSE PROPORTION, or RATIO. 

 See Ratio. 



INVOLUTE OF A CURVE. See Curves. 



IRON, CARBURET OF. See Carbon. 



ISOCHROMATIC, &c. See Gloss. I. 



ISODYNAMIC, having equal power. 



JARGON. See Zircon. 



LATENT HEAT. See Caloric. 



LAW OF THE SINES. See Refractive 

 Power. 



LENS POLYZONAL. See Polyzonal. 



LEVEL. See Gloss. I. 



LEUCOCYOLITE, a name given to a va- 

 riety of Apophyllite, which see. 



LEVER (Latin levare, and French lever, 

 to lift, or raise) is one of the mechanical 

 powers. It is an inflexible bar, supported 

 and moveable in one point of its length 

 on a pivot, or prop, called the fulcrum. 

 One end of the lever is applied to the 

 weight to be raised, while a force is ap- 

 plied to the other end. The power of 

 this instrument depends on the proportion 

 between the lengths of the parts of the 

 lever on each side of the fulcrum. See 

 Balance. 



For a plain account of the different kinds 

 and applications of levers, see Popular 

 Introductions, pages xx. xxiv. 



LEYDEN PHIAL. The Lcyden Phial, or 

 Leyden Jar, (so called because it was first 

 constructed in that city,) is a cylindrical 

 glass vessel, coated to a certain height, 

 inside and outside, with some conducting 

 substance, which is capable of being 

 charged with electrical fluid, accumulated 

 for various experiments. A combination 

 of such phials is an electrical battery. 

 See those words in the Index for more 

 complete explanation. 



LIGHT, RAYS OF REFLEXION OF, 

 &c See Gloss. I. 



LIGNUM NEPHRITICUM (Latin %- 

 num, wood, and Greek nephros, a kid- 

 ney) is a bitter tasted wood, so called 

 because it was once believed to be a sove- 



