#00 OUTLINES OF NATURAL PHILOSOPHY. 



SECT. XII. 



OF THE ABERRATION OF LIGHT, ANP 'THE NUTA- 

 TION OF THE EARTH'S AXIS. 



Aberration of Light. 



09- IF a ray of Light, coming in a straight 

 line, and with a given velocity, pass through a 

 tube, also moving in a straight line, with a gi- 

 ven velocity, and remaining parallel to itself; 

 the path of the ray, relatively to the tube, is the 

 diagonal of a parallelogram, the sides of which 

 are proportional to the velocities "of the Light, 

 and of the tube, and in the same straight lines, 

 one of the velocities only, being estimated in a 

 direction opposite to its own. 



This is evident from the composition of motion. 



We may conceive what is here supposed to be ac- 

 tually the case, with a ray of light coming from a 

 fixed star, and passing through a telescope, or a 

 tube, furnished with plain sights ; the tube having 

 the same motion with the earth in its orbit, which, 

 for a short time, may be regarded as rectilineal and 

 uniform. The path of the ray in the tube, is 



therefore 



