[ '263 ] 



VII. On t/ie Dispersion in Artificial Double Refraction. 



By L. N. G. FILON, Af.A., D.Sc., Fellow and Lecturer in Mathematics of University 



College, London. 



Communicated by Professor F. T. TROUTOK, F.R.S. 

 Received January 25, Read February 28, 1907. 



SUMMARY OK CONTENTS. 



Page 



1. Introduction 264 



PART I. 

 THEORY OF THE EXPERIMENT AND DISCUSSION OF THE VARIOUS ERRORS. 



2. Simple theory of the experiment 265 



3. Description of the apparatus - 268 



4. Effect of introducing the polarizing Nicol 27:? 



5. Effect of finite breadth of the source 274 



6. Effect of relative rise and fall of the two beams and of elastic yielding of the bed-plate and 



knife-edges 274 



7. Influence of obliquity on relative retardation 275 



8. Combined effect of flexure and obliquity - .... 276 



9. Imperfect adjustment of the inclination of the slit . . 277 



$ 10. Imperfect horizontal adjustment of the knife-edges 277 



$11. Imperfect vertical adjustment of the knife-edges 278 



12. Error due to weight of beams themselves 27R 



13. Error due to imperfect annealing 27H 



PART II. 



EXPERIMENTAL RESULTS. 



14. Glasses observed ^>7; 



15. Linear law connecting A. and the stress 280 



16. Significance of this linear law 284 



17. Methods of reduction 287 



18. Tables of results 289 



19. Discussion of the values of AO, &W U 29* 



20. Systematic residuals 293 



21. Possible explanation by absorption bands 297 



22. Determination of absolute values of C 301 



23. Effect of chemical composition on stress-optical properties 302 . 



24. Failure of HOOKE'S law for glass 2783 303 



25. Conclusion 305 



VOL. CCVII. A 419. 26.7.07 



