154 POPULAR LECTURES AND ADDRESSES. 



7\ to 4 nearly, or 3*9. You may say then, roundly, 

 that for the wave-lengths of visible light, which 

 alone is what is represented on that table, we 



TABLE I. DATA FOR VISIBLE LIGHT 



have wave-lengths of from 4 to 8 on our scale 

 of i/ioOjOOOth of a centimetre. The 8 is in- 

 visible radiation a little below the red end of the 



