Diffraction Fringes and Micrometric Observations. 441 



Fig. 3. — Instantaneous Form of Wave-Train for &='3/7r, whence 

 R'VR' = ] -0.54. 







wmmm 































the experiments just referred to the frequency was '65 X 10° 

 per second, and R'/R became 31*6. Hence R"/R has the 

 value 31*6 x 1-054=33-3 nearly. Thus, writing e - w ^ 2Lv for 

 the attenuator of the waves along the wires instead of 

 4f g -EV/2L» " ncreases the index by about five and a half per cent., 

 and so brings it by that amount nearer to the value deter- 

 mined experimentally. 



Univ. Coll., Nottingham, 

 Nov. 29, 1898. 



XLI. On certain .Diffraction Fringes as applied to Micro- 

 metric Observations. By L. N. Gr. Filon, M.A., Demon- 

 strator in Applied Mathematics and Fellow of University 

 College, Londonf. 



1. rTVEE following paper is largely criticism and exten- 

 X sion of Mr. A. A. Michelson's memoir "On the 

 Application of Interference Methods to Astronomical Obser- 

 vations," published in the Phil. Mag. vol. xxx. p. 256, March 

 1891. 



* See Equation (2) p. 301, Phil. Mag. Sept. 1898. 



t Communicated by the Physical Society : read November 2o, 1898. 



