488 



NOTES. 



NOTE 164, p. 125. A tetrahedron is a solid contained by four triangular sur- 

 faces, as fig. 40 : of this solid there are many varieties. 



NOTE 166, p. 126. 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 166, pp. 126, 215. A rhombohedron is a solid contained by six plane 

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

 parallel to 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 167, P. 127. Sublimation. Bodies raised into vapour which is again 

 condensed into a solid state. 



Fig. 41. 



NOTE 168, p. 128. The surface of a column 

 of water, or spirit of wine, in a capillary tube, 

 is hollow ; and that of a column of quicksilver 

 is convex, or rounded, as in fig. 41. 



NOTE 169, p. 128. Inverse ratio, $c. The elevation of the liquid is greater 

 in proportion as the internal diameter of the tube is less. 



NOTE 170, p. 129. In fig. 41, the line c d shows the direction of the resulting 

 force in the two cases. 



NOTE 171, p. 129. When two plates of glass are brought near to one another 

 in water, the liquid rises between them; and, if the plates touch each other 

 at one of their upright edges, the outline of the water will become an hyper- 

 bola. 



NOTE 172, p. 130. Let A A', fig. 42, be two plates, both of which are wet, 

 and B B', two that are dry. When partly immersed in a liquid, its surface will 



Fig. 42. 



be curved close to them, but will be of its usual level for the rest of the distance. 

 At such a distance, they will neither attract nor repel one another. But, as 

 soon as they are brought near enough to have the whole of the liquid surface 



