Light. 143 



fire, a torch, or candle, &c. &c.: they are re- 

 flected or sent back by what are termed opdke 

 bodies, or those which have no power of affording 

 light in themselves. 



3. Light, whether emitted or reflected, always 

 moves in straight or direct lines ; as may easily 

 be proved by looking into a bent tube, which 

 evidently obstructs the progress of the light in 

 direct lines ; and proves that the theory of recti- 

 linear emission is free from the objections which 

 lie against the hypothesis of the undulatory mo- 

 tion of light. 



4. By a ray of light is usually meant the least 

 particle of light that can be either intercepted or 

 separated from the rest. A beam of light is ge- 

 nerally used to express something of an aggregate 

 or mass of light greater than a single ray. 



5. Parallel rays are such as proceed equally 

 distant from each other through their whole 

 course. The distance of the sun from the earth 

 is so immense, that rays proceeding from the 

 body of that luminary are generally regarded as 

 parallel. 



6. Converging rays are such as, proceeding 

 from any body, approach nearer and nearer to 

 each other, and tend to unite in a point. The 

 form of rays thus tending to a union in a single 

 point has been compared to that of a candle-ex- 

 tinguisher ; it is in fact a perfect cone. 



7. Diverging rays are those which, proceed- 



