SCIENTIFIC TERMS. 145 



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

 flection. For the effects of Mirrors, see page 1 8. 



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

 is of a brittle nature, and has been procured only in small quantities. 



Muriates, the combination of a base with muriatic acid. 



Muriatic Acid, a powerful acid obtained from sea-salt. It is much used 

 in the arts. 



Matron, a salt found at different parts of the earth, either on or near 

 its surface. It is the nitre of the ancients, but is very different from 

 our nitre, the latter being a nitrate of potash, and the former a 

 carbonate of soda. 



Xeutral Salt, a salt in which the acid is completely neutralized by the 

 base, and the base by the acid. 



Xickel, a wbite 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. 



Citric Acll, a powerful acid, obtained from nitre or saltpetre, by 

 distilling it with sulphuric acid. It is much used in the arts. Ni- 

 trous Acid is of a similar nature to the former. The salts are Xi- 

 trates and Nitrites. 



Nitrogen or Azote, one of the constituent parts of the atmosphere. 

 See page 73. 



Nitro-Muriatic-Acid. See Aqua-Regia. 



Nitrous Oxide Gas, commonly called Laughing-gas. See page 78. 



Ochre, & combination of an earth with an oxide of iron. 



Olefiant Gas, a kind of carburetted hydrogen. See page 77. 



Onyx, a precious stone of the agate kind. 



Opal, a precious stone of which there are various kinds and different 

 colours. 



Ophites, a stone resembling a serpent, from which it takes its name. 



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 re- 

 semblance to sulphate of magnesia (Epsom salts) persons have oc- 

 casionally been poisoned with it It is used in the arts. 



Oxide, a substance combined with oxygen. 



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

 page 72. 



Oxygenate, to acidify a substance with oxygen. 



Oxymuriatic Acid Gas, same as Chlorine. 



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 56. 



Parhelion, a mock sun. See page 56. 



Pendulum, a heavy body, so suspended that it may swing backwards 

 and forwards. A second's pendulum, or a pendulum that will make 



a 



