Energy in the Electromagnetic Field. 31 



lines is indicated in fig. 7, which has been drawn for a large- 

 value (0*5 inch) of X for convenience of representation. 



Fig. 7. 



. ty V >' V 



The lines of flovr of energy in relation to the loci of minimum illumin- 

 ation in the Diffraction Field due to a straight edge. 



6. Summary and Conclusion. 



The present paper deals with the distribution and flowrof 

 energy in the immediate neighbourhood of a perfectly 

 reflecting cylinder on which plane light waves are grazingly 

 incident in a direction at right angles to its axis. The 

 following are the principal results which are indicated by 

 theory and have been verified by photometric study of the field.. 



(a) The positions of maxima and minima of illumination 

 are determined by eliminating from the pair of equations 



2y0 + Za0 2 j2=x ; 20 2 (y + a0) = m\/2 ; 

 or from the pair of equations 



2y0 + 3a0 2 2 = as j 20 2 (y + aO) = mX/2 - eX/2ir t 



