412 Ewell — Gilds' Geometrical Presentation of the 



Art. XXXYI. — Gibbs* Geometrical Presentation of the Phe- 

 nomena of Reflection of Light • by Arthur W. Ewell. 



In his lectures at Yale upon the Electromagnetic Theory of 

 Light, Prof. Gibbs briefly outlined a geometrical method of 

 representing and interpreting the phenomena of total and 

 metallic reflection, which, to the writer's knowledge, has never 

 been published, and is not included in his collected papers. 

 The writer has found this method so valuable in teaching and 

 in experiments upon metallic reflection, that he believes others, 

 outside the small number who were privileged to hear Prof. 

 Gibbs, will find it a clear, simple and practical method of 

 representing the relative amplitude and phases and optical 

 constants, the analytical expressions for which are complicated. 



The foundations of this paper are lecture notes of the years 

 1898-99. In. place of Prof. Gibbs' vector notation, the more 

 common scalar quantities will be used, and the writer has added 



extensions of this method to the simpler cases of reflection, 

 applications to the determination of refractive indices, coeffi- 

 cients of absorption, and reflecting power, and numerical 

 illustrations. 



