148 VOCABULARY OF SCIENTIFIC TERMS. 



Tellurium, a metal discovered in the year 1798. It forms combina- 

 tions with various bodies, but it has not yet been used except for 

 experiments. 



Thermometer, an instrument for discovering the temperature of the air. 



Tin, a well known white metal, and very little inferior in appearance 

 to silver. It has but very little affinity for oxygen, for which reason 

 our culinary vessels are coated with a solution of it. 



Topaz, a gem of a gold colour, called by the ancients chrysolite. The 

 finest topazes come from the East Indies, the Great Mogul is said to 

 have had one worth 20,000. 



Trumpet, Speaking and Hearing. See pages 51 and 52. 



Tungsten, a very heavy metal, when pure it is extremely hard and 

 brilliant. It is of very little use. 



Uranium, a metal discovered in the year 1786. It is hard and brittle, 

 but is found in very small quantities, and is of no particular use. 



Vacuum, a space void of matter. 



Valve, in hydraulics a kind of cover of a tube so contrived as to admit 

 a fluid one way and by its pressure to prevent its return. 



Vision. See page 28. 



Voltaic Electricity, or " Galvanism." See page 64. 



Water. For the various kinds of this fluid, seepage 41. 



Wind, air in motion. See page 57. 



Yttria, a kind of earth discovered in Sweden at the latter end of the 

 last century. 



Zaffire, the oxide of cobalt, used for painting porcelain a blue colour. 



Zero, a term applied to a certain point in the thermometer ; in Fah- 

 renheit's thermometer, it is placed at 32 below the freezing point. 

 In Reaumur's, as also in the French centigrade thermometer, it is 

 placed at the freezing point. 



Zinc, a well known metal. It is never found in a pure state, but 

 principally obtained from calamine and blende. Zinc is naturally 

 brittle, yet when heated and annealed, it may be passed through 

 rollers and formed into sheets. This is one of the most useful 

 alloys, principally in combination with copper. It is also used in 

 medicine. 



Zirconia, a new kind of earth, first discovered in the Jargon or Zir- 

 con of Ceylon. 



