PHYSICS OF THE NINETEENTH CENTTRY.- LIGHT. 467 



Exterior Fringes produced by Homogeneous Red Light. 



Interior Bands produced by Homogeneous Red Light. 



The reader has now been made acquainted with one of the chief 

 experimental bases of the undulatory theory of light, and a few of the 

 actual measurements of the phenomena and of the results deduced 

 from the theory alone have been been placed side by side, that the 

 degree of correspondence may be seen. The measured positions in 

 the first table differ from those calculated but very little, the greatest 

 difference being with regard to the bands of the first order, that is, for 

 the first bands F, F', outside of the shadow. The reason is that 

 these bands are broader than the others, etc., and therefore it is 

 more diffcult, in taking the measurement, to fix precisely upon the 



30 2 



