14 INTRODUCTION. 



SECTION III. OF SPACE. 



54. Definition. A solid is a portion of space limited 

 ill magnitude on all sides. 



Scholium. Space is a mode of existence incapable of definition, 

 and supposed to be understood by tradition. 



55. Definition. A surface is the limit of a solid. 



56. Definition. A line is the limit of a.surface. 



57. Definition. A point is the limit of a line. 



Scholium. The paper, of which this 

 figure covers a part, is an example of a 

 solid, the shaded portion represents a 

 portion of surface : the boundaries of that surface are lines, and the 

 tliree terminations or intersections of those lines are points. In con- 

 formity with this more correct conception, these definitions are 

 illustrated by representations of the respective portions of space of 

 which the limits are considered ; and also by the more usual method 

 of denoting a line by a narrow surface, and a surface by such a line 

 surrounding it. 



58. Definition. A line joining two points is called 

 their distance. 



59. Definition. When the distance of any two or 

 more points remains unchanged, they are said to be at 

 rest; and a space of which all the points are at rest, is 

 a quiescent space. 



60. Definition. A line which 



must be wholly at rest, with respect to any quiescent space, 

 when two of its points are at rest in that space, is 

 a straight line. 



^ iTwii ^"y ^^ (51, Definition. A line 

 which is neither a straight line, nor composed of straight 

 lines, is a curve line. 



