EXPLANATION OF SCIENTIFIC TERMS. 



11 



in all temperatures, and in this they 

 diff**' from vapours. See Fapour. 



l*S signifies that the substance 

 spoken of has the nature of gas; and 

 thus gaseous fiuids are distinguished from 

 other fluids. 



GLAUBERITE is a crytallized salt com- 

 posed of nearly equal parts of sulphate of 

 lime and sulphate of soda, both anhy- 

 drous, or nearly so. It was so called, iu 

 honour of Glauber, whose name is also 

 given to Glauber salts, or sulphate of 

 soda. Glauberite is found among the 

 pieces of rock salt brought from South 

 America. 



GONIOMETER (from the Greek gonia, 

 an angle) is an instrument for measuring 

 angles. Such an instrument is particu- 

 larly requisite in measuring the solid an- 

 gles of crystals. That of the late Dr. 

 Wollaston is peculiarly ingenious. 



GOVERNOR, an addition applied to cer- 

 tain machines for the purpose of equaliz- 

 ing their motion. It is a centrifugal 

 power, like that of the fly-wheel, and is 

 described at large at page 52, 3IECHA- 

 xics, Treatise ii. 



GRAVITY ( Latin gravitas, heaviness) is 

 a name given to that tendency which 

 bodies have to fall to the earth, or rather 

 towards its centre. The abstract power, 

 or unknown cause, by which these phe- 

 nomena are produced, is termed Gravita- 

 tion. and this power is supposed to act 

 throughout nature, so that all bodies, as 

 well as the particles of the same body, 

 have a tendency to approach each other, 

 in proportion to their masses, but lessen- 

 ing in force as the squares of the dis- 

 tances between the centres of the several 

 masses are increased. Gravity and At- 

 traction are often used synonymously. 

 Both are abstract names for the same 

 unknown power; but the latter is ap- 

 plied more generally : we speak, for ex- 

 ample, of capillary attraction, and mag- 

 netic attraction, but not of capillary or 

 magnetic gravity. 



GRAVITY, CENTRE OF, is a point in 

 a body from which, if that body could be 

 suspended, the whole body would remain 

 at rest, (with respect to its tendency to 

 the earth,) in whatever respective posi- 

 tion the surrounding parts may be turned. 

 Thus, the centre of gravity of a globe is 

 its common centre, and that of a balanced 

 beam is the pivot on which it turns. 



RELATIVE. See Gravity, 



Specific. 



SPECIFIC. The comparative 



or relative gravities of different bodies 

 towards the earth are measured by a 

 general standard termed weight , and one 

 substance is said to have a greater specific 

 gravity than another, when a less portion 

 of its bulk is of equal weight to that 

 other. Thus, a cubic inch of platina is 

 nearly twice the weight of a cubic inch 



of silver ; and, therefore, is said to have 

 double its specific gravity, the specific 

 gravity of platina is to that of silver as 2 

 to 1. 



GRAVITY, LINE OF DIRECTION 

 OF, is that line which passes through 

 the centre of gravity of a body iu a 

 direction to the centre of the earth. 



GYRATION (Latin gyrus, a circle) is the 

 action of turning round in the manner of 

 a wheel. 



CENTRE OF. See Oscil- 



lation. 



CIRCLE OF. See ditto, 

 luminous, and sometimes 

 appearing occasionally 



HALO, 



coloured circle, 



around the heavenly bodies, but more 

 especially about the sun and moon." 

 See Parhelia. 



HARDNESS is the resistance to impres- 

 sion. It is incompressibility, but limited 

 to solids. See Compressibility. 



HEAT. See Caloric. 



CAPACITY FOR. See Caloric, 



Capacity for. 



CONDUCTORS OF. See Con- 



ductor. 



LATENT. See Caloric, Latent* 



RADIATION OF. See Radia- 

 tion. 



SPECIFIC. See Caloric, Spe- 

 cific. 



HERMETIC SEAL. The origin of che- 

 mistry has been ascribed to the Egyptian 

 Hermes, and, therefore, termed the Her- 

 metic Art. When the neck of a glass 

 vessel, or tube, is heated to the melting 

 point, and then twisted with pincers until 

 it be air-tight, the vessel, or tube, is said 

 to have received the seal of Hermes to 

 be Hermetically sealed. 



HETEROGENEOUS. See Homogene- 

 ous. 



HEXAHEDRON. See Rhombus. 



HOMOGENEOUS (from the Greek ho- 

 mos, alike, and genos, kind) designates 

 such substances as have their particles all 

 of the same nature, and, consequently, 

 possessing the same properties. Hetero- 

 geneous, on the contrary (Greek heteros, 

 different) denotes that the substance 

 which it denominates is made up of parts 

 that have different qualities. Thus, in 

 minerals, the diamond is a homogeneous, 

 and granite is a heterogeneous body. 



HYACINTH. See Zircone. 



HYDRATES. Chemical compounds (par- 

 ticularly salts) which contain water as 

 one of their ingredients, have been 

 termed hydrates. If water be not a con- 

 stituent, they are said to be dnhydroiis, 

 which signifies without water ; from the 

 Greek privative a and hydor water. 



HYDROUS, watery, or containing water 

 in its composition. 



HYPERBOLA. See Cone, and Conic 

 Sections. 



HYPERBOLOID. See Conoid. . 



