142 VOCABULARY OF 



Flux, a substance mixed with any mineral to promote its fusion \ 

 thus 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. 



Freezing, the fixing of a fluid body into a solid mass, through the ab- 

 straction of its caloric. See page 16. 



Friction, in Mechanics, implies the resistance arising from the rough- 

 ness of the surfaces of the moving bodies. See page 70. 



Fulcrum, in Mechanics, is the point about which a lever moves. 



Fusion, the state of a solid body rendered fluid by heat. 



Galvanism, the science of annual electricity. See page 64. 



Garnet, a precious stone of a red colour. 



Gas, the state of any permanently elastic fluid. See page 71. 



Gasometer, a vessel for measuring, collecting, or containing gas. 



Gelatin, an animal substance ; jelly. 



Geology, that part of Natural History which treats of the structure of 

 the earth. See page 78. 



Glucine, a peculiar earth, so named from its sweetness. 



Gold, a well-known metal found in almost every country of the world. 

 South America furnishes the greatest quantity of gold now used, 

 although various parts of Hindostan are very rich in it. Gold is 

 obtained in a more pure state than any other metal, and, with the 

 exception of platinum, is the heaviest of all metals. It is so ex- 

 ceedingly ductile, that a cube of one inch and a quarter would gild 

 a wire of sufficient length to extend round the earth. Gold has no 

 affinity for the oxygen of the atmosphere, and therefore will not 

 rust ; it is also considered' a perfect metal, for if kept in a state of 

 fusion for a very considerable time, it will sustain but a very trifling 

 loss of weight. 



Granulation, the operation by which metallic substances are reduced 

 into small pieces. This is performed by pouring the melted metal 

 slowly into water, while kept in a state of agitation. 



Gravimeler, another term for the Aerometer or Hydrometer. 



Gravitation, the tendency of bodies towards the centre of the earth. 

 See page 1 1. 



Gravity, Specific, the relative weight of different bodies compared 

 with some well-known body. Water is generally used for this pur- 

 pose, and the specific gravity of any body denotes that such body is 

 so many times heavier than water, bulk for bulk. Thus the specific 

 gravity of platinum is 21, of gold 19, of mercury 13-6, of lead 11, 

 of silver 10, of cobalt 87, of manganese 8, of iron 7'7, of tin 7, 

 of zinc 7, of antimony 6-7. See page 46. 



Grotto del Cano, a grotto in Italy, which takes its name from the 

 number of dogs killed there through suffocation. See page 73. 



Gryphite, an oblong fossil shell increasing in width from the head to- 

 wards the extremity where it terminates in a curve or circle. 



Gypsum, sulphate of lime, selenite or plaster of Paris. 



Hail, water congealed during the act of falling. See page 55. 



Halo, or Corona, a coloured circle sometimes appearing round the sun 

 or moon. See page 55. 



