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II. On the Flow of Energy in the Electromagnetic Field 

 surrounding a Perfectly Reflecting Cylinder. By T. K. 

 Chinmayam, B.A. (Hons.), Research Scholar in the Indian 

 Association for the Cultivation of Science , Calcutta*. 



[Plate I.] 

 1. Introduction. 



IN a paper recently contributed to this Journal, Mr. N. 

 Basu t has discussed the general features of the pheno- 

 mena observed in the immediate neighbourhood of a perfectly 

 reflecting cylinder on which plane light waves are incident 

 in a direction at right angles to its axis. Further investi- 

 gation was, however, necessary in order to establish the 

 formulae for the distribution of light intensity in the various 

 parts of the field. These formulae have now been obtained 

 and subjected to a detailed experimental test. Besides 

 describing the results of a photometric study that has been 

 carried out, the present paper also deals with the form of the 

 lines of flow of energy through the field which, it is thought, 

 may prove of interest with reference to the work of Profs. 

 K. W. Wood % and Max Mason § on the simpler case of the 

 interference field due to two-point sources of light. 



It may be remarked here that the phenomena which form 

 the subject of this paper may be strikingly shown on a large 

 scale without the aid of a microscope by using a cylindrical 

 surface of very large radius as the diffracting " edge." A 

 strip of thick plate glass, two inches wide and about a yard 

 long, may be bent into a circle of some yards radius by 

 resting it on supports near the two ends and loading the 

 latter sufficiently. A slit illuminated by a Cooper-Hewitt 

 lamp and placed at some distance from the surface in a line 

 with it, may be used as the source of light. A very large 

 number of fringes may then be seen with a low-power eye- 

 piece if the plane of observation be within a few feet of the 

 cylindrical " edge." At greater distances, the fringes widen 

 out; their visibility and number decrease, and their spacing 

 alters with increasing distances from the cylinder in such 

 manner as to approximate more and more closely to that of 



* Communicated by Prof. C. V. Eaman, M.A. 



t N. Basu: "On the Diffraction of Light by Cylinders of large radius." 

 Phil. Mag\ xxxv. p. 79 (1918). 



% ft. W. Wood : " On the Flow of Energy in a System of Interference 

 Fringes." Phil. Mag. vol. xviii. p. 250 (1909). 



§ Max Mason : "The Flow of Energy in an Interference Field." 

 Phil. Mag. vol. xx. p. 290 (1910). 



