GEOMETRY. 849 



spot, of a very sensible length and breadth; and 

 our not being able to measure its dimensions with 

 the naked eye, arises only from its smallness. 

 The same reasoning may be applied to every thing 

 that is usually called a point ; even the point of 

 the finest needle appears like that of a poker when 

 examined with the microscope. 



2. A line is length, without breadth or thick- 

 ness. What was said above of a point, is also ap- 

 plicable to the definition of a line. What is drawn 

 upon paper with a pencil or pen, is not, in fact, a 

 line, but the representation of a line. For how- 

 ever fine you may make these representations, they 

 will still have some breadth. But by the defini- 

 tion, a line has no breadth whatever ; yet it is im- 

 possible to draw any thing so fine as to have no 

 breadth. A line, therefore, can only be imagined. 

 The ends of a line are points. 



3. Parallel lines are such as always keep at the 

 same distance from each other, and which, if pro- 

 longed ever so far, would never meet. PI. 3. 

 Fig. 1. 



4. A right line is what is commonly called a 

 straight line, or that tends every where the same 

 way. 



5. A curve is a line which continually changes 

 its direction between its extreme points. 



6. An angle is the inclination or opening of two 

 lines meeting in a point, Fig. 2. 



7. The lines A B, and B C, which form the an- 

 gle, are called the legs or sides j and the point 

 B where they meet, is called the vertex of the 

 angle, or the angular point. An angle is some- 

 times expressed by a letter placed at the vertex, 

 as the angle B, Fig. 2 : but most commonly by 

 three letters, observing to place in the middle the 



