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PHYSICAL SCIENCES. 



NOTE 162, p. 106. Analytical formula or expression. A combination' 

 of symbols or signs expressing or representing a series of calculation, and 

 including every particular case that can arise from a general law. 



NOTE 163, p. 106. Fig. 38 is a perfect octahedron. Sometimes its 

 angles, A, X, a, a, &c., are truncated, or cut off. Sometimes a slice is cut 

 off its edges A a, X a, a a, &c. Occasionally both these modifications take 

 place. 



NOTE ] 64, p. 1 07. Prismatic crystals of sulphate of nickel are some- 

 what like fig. 62, only that they are thin, like a hair. 



NOTE 165, p. 108. Zinc, a metal either found as an ore or mixed with 

 other metals. It is used in making brass. 



NOTE 166, p. 108. A cube is a solid contained by six plane square 

 surfaces, as fig. 39. 



Fig. 39. NOTE 167, p. 108. A tetrahedron is a solid con- 



tained by four triangular surfaces, as fig. 40 : of this 

 solid there are many varieties. ' 



NOTE 168, p. 108. There are many varieties of the 

 octahedron. In that mentioned in the text, the base 

 aaaa, fig. 38, is a square, but the base may be a 

 rhomb ; this solid may also be elongated in the direction 

 of its axis A X, or it may be depressed. 



NOTE 169, pp. 109, 192, 273. A rhombohedron is a solid contained by 

 six plane surfaces, as in fig. 63, the opposite planes being equal and similar 

 rhombs parallel to one another ; but all the planes are not necessarily equal 

 or similar, nor are its angles right angles. In carbonate of lime the angle 

 C A B is 105-55, and the angle B or C is 75-05. 



NOTE 170, p. 109. Sublimation. Bodies raised into vapour which 

 is again condensed into a solid state. 



NOTE 171, p. 112. Platinum. The heaviest of metals; its colour is 

 between that of silver and lead. 



NOTE 172, p. 113. The surface of a column of water, or spirit of 



