GEOMETRY. 349 



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 thi:ig 

 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 li?ie 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 tliese 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. 



o. 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 ; and the point 

 B where they meet, is called the vertex of the 

 angle, or the aiigular 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 



