Coral Rocks, See page 86.

Crucible, a small vessel used in chemistry for melting metals and

other purposes.

Crystallization, an operation in which various earths, salts, &c., pass from a fluid to a solid state.

Cyanogen, Prussic acid, a most virulent poison.

Decomposition, the reducing a body into its simple elements.

Deliquescence, a term applied to saline bodies becoming moist or liquid through their affinity for the aqueous matter contained in the atmosphere.

Dew, a kind of mist which falls when the sun is below the horizon. See page 53.

Diamond, the most valuable, pellucid, and hard of all the minerals. See page 85.

Diaphanous Body, a body through which the rays of light can pass. Dioptrics, the science of refracted vision. See page 26.

Discharger, an instrument used in electricity for the purpose of discharging any excited body.

Distillation, that process whereby the most subtle parts of a compound body are separated by the means of caloric from the mass, in a state of vapour.

Divergent, a term in optics to express rays of light receding from each other; concave glasses make the rays diverge, while convex glasses make them converge.

Diving Bell, a machine by means of which any person may descend to a considerable depth below the surface of the water.

Dynamics, the science of the motion of bodies.

Earths, certain bodies which are incombustible and generally unalterable by fire.

Echo, reflected sound. See page 49.

Effervescence, that motion which takes place in certain liquids through the escape of a gaseous substance.

Elastic fluids, a name given to vapours and gases. Vapour is an elastic fluid, but it may be condensed. Gas is a permanently elastic fluid because it cannot be readily condensed.

Electric, a body which may be easily excited by electricity, as resin, silk, wood, &c.

Electricity. See page 56.

Electrometer, an instrument to measure electricity. See page 61. Electrophorus, an electrical instrument for showing perpetual electricity. See page 60.

Eudiometer, an instrument for measuring the purity of the air. Evaporation, that act by which fluids are converted into vapours by heat. See page 51.

Eye, explained. See page 27.

Fermentation, an intestine motion arising spontaneously among the small and insensible particles of a mixed body, producing a different combination of those parts: there are three kinds, acetous, vinous, and putrefactive.

Flame, volatile inflammable matter in the act of combustion, and emitting a copious light.

L

Fluoric Acid, a peculiar acid obtained from fluor spar; it is the only acid that will corrode glass.

thus

Flux, a substance mixed with any mineral to promote its fusion;
an alkali is mixed with silica or sand, to form glass.
Focal-distance, the distance from the centre of the glass to the focus.
Focus, in optics, a central point where rays of light converge.

Fossil-remains, those animal and vegetable remains of the earliest times which have preserved their original forms. See page 87.

Freezing, the fixing of a fluid body into a solid mass, through the abstraction of its caloric. See page 15.

Friction, the act of rubbing bodies together; in mechanics it implies the resistance arising from the roughness of the surfaces of the moving bodies. See page 68.

Fulcrum, in Mechanics, is the point about which a lever moves. Fusion, the state of a solid body rendered fluid by the application of heat.

Galvanism, the science of animal electricity. See page 62.

Gas, the state of any permanently elastic fluid. See page 69.
Gasometer, a vessel for measuring, collecting, or containing gas.
Geology, that part of Natural Philosophy which treats of the structure
of the earth. See page 76.

Gold, a well known metal. See page 80.

Gravimeter, another term for the Areometer, or Hydrometer.

Gravitation, the tendency of bodies towards the centre of the earth. See page 10.

Gravity, Specific, the relative weight of different bodies compared with some well known body, as water. See page 44.

Grotto del Cano, a grotto in Italy, which takes its name from the number of dogs killed there through suffocation. See page 71. Hail, water congealed during the act of falling. See page 53.

Halo, or Corona, a coloured circle sometimes appearing round the sun or moon. See page 54.

Heat, the sensation caused by the action of fire.
Helioscope, a peculiar kind of telescope.

Hydrates, those substances which have such an affinity for water as to solidify it. Slaked lime is a hydrate of lime.

Hydraulics, that science which teaches the velocity and force of fluids in motion. The construction of water engines of all kinds depends on Hydraulics. See page 45.

'Hydrogen, one of the constituents of water. See page 73.

Hydrometer, an instrument to show the strength of spirits.

Hydrostatic-Balance, an instrument for ascertaining the specific gravity of bodies. See page 45.

Hydrostatics, that science which teaches the weight and pressure of fluids. See page 43.

Ice, the state of water deprived of its caloric.

Ignis-fatuus, a meteor occasionally seen in marshy places. See page 55.

Iodide, a compound formed by the union of Iodine with any substance. For Iodine, see page 20.

Iridium, a newly discovered metal, so named from Iris, the rainbow, in

consequence of the different colours its salts assume. It is not much used.

Iron, a well known metal. See page 82.

Lead, a well known metal. See page 81.

Lens, a piece of glass or other transparent body whose sides are either convex or concave, for the purpose of converging or diverging the rays of light.

Lever, a bar of iron or wood, used as one of the mechanical powers. See page 64.

Leyden Phial, or Jar, a glass jar, coated with tin foil, for electrical purposes. It received its name from the first contriver being a native of Leyden. See page 59.

Light, that power by which objects are made perceptible to our sense of seeing. See page 23.

Lightning, an electrical phenomenon preceding thunder.

Lithium, a recently-discovered metal, brought from Sweden. It is of no practical use.

Liquid, the state of any body, in which, by means of heat, the particles slide over one another, and wet any substance that comes in contact with it. Water, oil, &c., are both liquids and fluids. Quicksilver is a fluid but not a liquid.

Machine, any body intended to produce motion, so as to save either time or strength.

Magnesium, the metallic base of magnesia.

Magnetism, the quality of a body rendered capable of attracting. See page 12.

Malleability, that property by which metals may be extended through hammering.

Manganese, a metal noted for its peculiar affinity for oxygen. See page 83.

Matrix, the substance in which ores are imbedded in the earth. Mechanical Powers, engines used for raising weights. See page 64. Meniscus, a glass, convex on one side, and concave on the other. Menstruum, any fluid that will dissolve hard bodies.

Mercury, another name for quicksilver, so called from its volatility. See page 79.

Metals, are bodies known by their weight, ductility, &c. There are said to be nearly forty kinds of metals; Platinum is the heaviest, and Potassium the lightest.

Metallic Oxides, metals combined with oxygen, when, from being combustible, they become incombustible.

Metallurgy, the art of extracting metals from the ore,

them.

and purifying

Meteorology, the doctrine of the various phenomena of the atmosphere. See page 51.

Microscope, an optical instrument, formed by the combination of lenses, to magnify small objects.

Mineral, any substance, either of a metallic, earthy, or saline nature. Mineralogy, the science which treats of the properties of unorganized bodies, or minerals.

Mirror, any smooth body which forms the images of objects by reflec

tion. For the effects of Mirrors in condensing and multiplying the sun's rays, see page 16.

Molybdenum, a metal obtained from a mineral found in Sweden;

it is

of a brittle nature, and has been procured only in small quantities. It forms alloys, but they are of little use.

Muriates, the combination of a base with muriatic acid.

Muriatic Acid, a powerful acid obtained from sea salt. It is muc used in the arts.

Neutral Salt, a salt in which the acid is completely neutralized by the base, and the base by the acid.

Nickel, a white metal, both ductile and malleable, but of difficult fusion. The oxide of this metal is used in the arts, and the metal itself is sometimes used in combination with other metals.

Nitric Acid, a powerful acid, obtained from nitre or saltpetre, by distilling it with sulphuric acid. It is much used in the arts. Nitrous Acid is of a similar nature to the former. The salts are Nitrates and Nitrites.

Nitrogen or Azote, one of the constituent parts of the atmosphere. See page 70.

Nitro-Muriatic-Acid. See Aqua-Regia.

Nitrous Oxide Gas, commonly called laughing-gas. See page 76.
Ochre, a combination of an earth with an oxide of iron.

Olefiant Gus, a kind of carburetted hydrogen. See page 75.

Optics, the science of vision.

Ores, metallic earths.

Oscillation, the vibration of a pendulum.

Osmium, a newly-discovered metal; it is insoluble in the acids, and has not been applied to any use.

Oxalic Acid, a peculiar acid found in sorrel; it may be also obtained from sugar. It is of a highly poisonous nature, and from its resemblance to sulphate of magnesia (Epsom salts) persons have occasionally been poisoned with it. Its combinations are used in the

arts.

Oxide, a substance combined with oxygen.

Oxygen, a component part of the atmospheric air, and of water. page 70.

Oxygenate, to acidify a substance with oxygen.

Oxymuriatic Acid Gas, same as Chlorine.

See

Palladium, a recently-discovered metal. It is hard, and of a white colour. It has been obtained only in small quantities, and has been scarcely applied to any use.

Paraselene, a mock moon. See page 54.

Parhelion, a mock sun. See page 54.

Pendulum, a beavy body, so suspended that it may swing backwards and forwards. A second's pendulum, or a pendulum that will make one oscillation in a second, should be 393 inches in length, reckoning from the point of suspension.

Petrifaction, an incrustation formed on any body by the deposition of earthy matter from water.

Pewter, an artificial metal, being a mixture of tin, lead, and brass.

Phosphorus, a simple combustible. See page 20. A phosphuret is a

combination of phosphorus with some other substance. Phosphates and phosphites are salts formed by the combination of a base with phosphoric and phosphorus acid.

Phosphuretted hydrogen gas. See page 75.

Photometer, an instrument for measuring the intensity of light.

Physics, the science of matter and bodies with their affections, motions, operations, &c.

Plano-convex, a term applied to a lens which has one side flat and the other convex.

Plano-concave, a term applied to a lens which has one side flat and the other concave.

Platinum, a metal noted for its weight and want of affinity for oxygen. See page 80.

Plumbago, a carburet of iron; black lead.

Pluviameter, an instrument for measuring the quantity of rain that falls. Pneumatics, the science which treats of the properties of the air. See page 33.

Pneumatic trough, a vessel for collecting gases.

Potash, the vegetable alkali. See page 21.

Potassium, the metallic base of potash. See page 21.

Prism, a glass wedge used to refract light and separate it into different colours.

Prussic Acid, a peculiar acid of a most poisonous nature, it is prepared from blood and animal substances. Prussian blue is iron combined with this acid.

Pump, a well-known instrument for raising water. See page 46.
Pyrites, a combination of sulphur with a metal.

Pyrometer, an instrument for measuring the higher degrees of heat.
Pyrophorus, a substance which ignites when exposed to the air.
Rain, water that falls from the clouds. See page 52.

Rainbow, a well known beautiful appearance in the heavens caused by the refraction and reflection of the rays of light.

Retina, that enlargement of the optic nerve on which any body we see is painted. See page 27.

Retort, a chemical vessel for distillation, &c.

Rhodium, a recently discovered metal of a white colour, and remarkable for its hardness and brittleness.

Salts, the combination of any base with an acid.

Silicum, the metallic base of silica or flint.

Silver, a well known metal. See page 79.

Siphon, a bent tube used for the purpose of drawing off liquors, &c. See page 46.

Snow, particles of water frozen in falling. See page 53.

Soda, the mineral alkali. See page 22.

Sodium, the metallic base of soda. See page 21.

Spectrum, an oblong image of light made by a prism. See page 29. Steel, iron combined with carbon.

Strontium, the metallic base of the earth strontites.

Sublimation, a process whereby certain substances are volatilized by heat and again condensed by cold into a solid form. Flowers of sulphur are made in this way.