MINEEALOGT. 



isosceles triangles. The base, b, b, 6, 1, is always a rectangle ; 



but the ratio of its two sides is variable, as are all the other 



dimensions of the figure (fig. 36) . 



7. The rhombic octohedron is contained under eight faces, 



which are similar scalene triangles, while the base, b, b, b, b, 

 is a rhomb. All its dimensions are variable 

 (fig. 37). 



8. The right square prism, which is a 

 six-sided figure, differing from the cube only 

 in its four lateral planes, c, c, c, c, being rect- 

 angles. The extreme or terminal planes, a, a, 

 are square. The term right denotes that the 

 lateral and terminal planes are inclined to 

 each other at a right angle. It is used in 



opposition to oblique, which signifies that the sides are 



not perpendicular, but form an oblique angle with the 



terminal planes (fig. 38). 



FIG. 37. 



FIG. 38. 



FIG 



9. The right rectangular prism differs from the preceding, 

 in the terminal planes, a, a, being rectangular instead of 

 square (fig. 39). 



10. The right rhombic prism differs from the preceding 

 only in its terminal planes being rhombs (fig. 40). 



FIG. 40. 



FIG. 41. 



11. The right rhomboidal prism differs from the preced- 

 ing form, in the terminal planes, a, a, being rhomboids 

 (fig. 41). 



12. The oblique rhombic prism ; in this form the terminal 

 planes, , a, are rhombic, and the lateral planes form an 

 oblique angle with them (fig. 42). 



