EFFECT OF LIGHT. ]9 



language can do justice to them, life itself is all too 

 short for expressing the admiration which they force 

 from a mind capable of even a very small portion of 

 reflection. A very simple arrangement of the two mo- 

 tions of the earth not only produces these variations in 

 the duration and position of the sun's daily appear- 

 ance, which make the year ever new with the change 

 of seasons ; but, taken in combination with the form 

 and composition of the different parts of the earth's 

 surface, brings about all the alternations of sunshine 

 and shower, of calm and tempest, of sultriness and 

 of snow. 



Every one must be aware, that if an opaque globular 

 body were placed opposite to a light, in the same way 

 that this earth is placed with regard to the sun, that 

 the light would irradiate one half of it ; and if both 

 remained stationary, the enlightened half would be 

 always the same ; that the centre would be the most 

 strongly illuminated in consequence of the light falling 

 perpendicularly upon the surface there ; and that the 

 light would diminish from thence gradually to the 

 boundary, around which it would be comparatively 

 weak and faint. Also that, if the opaque body were 

 made to revolve round the luminous one, always pre- 

 senting the same side to it, the distribution of light 

 would still be the same, only if the distance were va- 

 ried during the revolution, the light would be more 

 intense when nearer, and more faint when more remote. 



If, however, the opaque body were made to turn 

 upon an axis, it would constantly shift the side pre- 

 sented to the light, unless one extremity of the axis of 



