EXPLANATION OF SCIENTIFIC TERMS. 



base, and tapering equally upwards until 

 it terminates in a point. Were the base 

 a right-lined figure, the solid would be 

 called a Pyramid ; and, in either case, all 

 lines drawn from the Periphery, or bound- 

 ing line of the base, to the top, (which is 

 termed the Apex or Vertex,) are straight 

 lines. 



The surface of a cone may be conceived 



Fig. 

 c 



as formed by the angular motion of a 

 straight line, one end of which moves 

 along the Circumference, or outline of the 

 circular base, while the other end con- 

 tinues either to touch, or to pass through 

 a fixed point above that base. The fol- 

 lowing explanation is applicable to each 

 of the annexed figures : 



Let the straight line A B (fig. 2.) be 



2. 



C. 



A 



so placed as to rise above the circle B a 

 D b, which it touches at B. Let 'the 

 end, B, of this line be moved along the 

 whole of the circumference B a D b, while 

 the same line always touches the fixed 

 point C. The line *C B will then have 

 marked out the surface of a cone C B D, 

 similar to the paper cones in the grocer's 

 shops. While the line C B has thus 

 traced the cone C B D, the other portion 

 of the line, C A, will have described an 

 inverted cone A C E, with its circular top 

 E c A d. These opposite cones are similar, 

 having the angles E C A and B C D, at 

 the common apex C, equal. Had the 

 line A B been unequally divided at C, 

 the two cones would have still been simi- 

 lar, but not equal. A right line, C 0, 

 drawn from the vertex C to the centre of 

 the base o, is termed the axis of the cone. 

 When this axis is at right angles to the 

 base, the solid is termed a Riyht cone ; 

 otherwise, as in the right-hand figure, it 

 is an Oblique, or Scalene cone. In the 

 former case, the sides C B and C D are of 

 equal length ; in the latter, they are un- 

 equal. 



CONGELATION is that state of certain 

 fluids in which they thicken and become 

 partially or wholly solid. Thus water, 

 at a certain temperature, is converted 

 into ice, and the skins of animals, when 

 dissolved in water by boiling, congeal in 

 cooling, and become glue. 



CONIC SECTIONS. Sections are cut- 

 tings ; and Conic Sections is a name for 

 that science which treats of the proper- 

 ties of certain curves that are formed by 



the cutting of a cone. If a cone be cut 

 by a plane parallel to the base, the section 

 (or flat surface of the cut) will be a circle; 

 and if it be cut by a plane passing through 

 the vertex, the section will be a triangle. 

 But neither the circle nor the triangle 

 are treated of, under the head of Conic 

 Sections ; because they belong to ordi- 

 nary Geometry. There are, however, 

 three other sections, the Ellipsis, the 

 Parabola, and the Hyperbola. 



I. 1. If the cone '(fig. 3.) be cut by a 

 plane which passes through both the 



Fig. 3. 



sides A B and A C, the outline of the 

 section will be an ellipsis. Or, if it be 

 cut in the direction cd, which cuts the 

 base, it will still be a portion of an ellip- 

 sis ; because this plane would meet the 



