L. P. Wheeler^ — Dispersion of Metals. 



493 



method or duration of polishing, or possibly (as is suggested by 

 the work of Lu miner and Sorge* on glass) they may arise from 

 different states of strain existing in the surface of different 

 samples of the same material. There seems to be, at least 

 tacitly, a general opinion that since Drude's specification of the 

 " normal " condition for a reflecting surface, it only requires 

 sufficient care in the preparation of a metallic mirror in order 

 to get consistent results ; and that consequently our knowledge 



Table I — Silver. 



Observer 



A 



n 



nk 



^ (10) - l2 



r 



n 2 (/c--l) 



A 



K 



Minor 



0-231// 



1-43 



Ml 



129 



15-7 



-0-80 



46-3 



47-1 



u 



•250 



1-49 



1-32 



125- 



15-4 



-0-47 



51-8 



52-3 



a 



•298 



1-56 



091 



53-6 



10-1 



-1-61 



49-5 



51-1 



a 



•346 



0-219 



1-10 



5-80 



3-41 



+ 1-16 



40-9 



39-7 



a 



•395 



0-155 



1-91 



4-81 



3-01 



3 64 



25-6 



220 



u 



•450 



0-164 



239 



4-29 



2-91 



5-67 



32-8 



27-1 



Tate 



•460 



0-270 



325 





• 





_ _ 





Minor 



•550 



0-169 



2-94 



3 V 9~7 



2 -74 



8 V 63 



38-1 



2~9 V 5 



Tate 



•500 



0-273 



356 















Minor 



•500 



0-176 



3-31 



3-50 



2-57 



10-9 



43-4 



32-5 



Tate.. 



•580 



0-284 



4-20 

















Drude 



•589 



0-181 



3-67 













Minor 



•589 



0-177 



364 



315 



2-44 



13 V 2 



47-0 



33-8 



Tate 



•620 



0-291 



4-52 













Drude 



•630 



0-203 



3-96 





_ 









Ingersoll _ 



•65 



0-154 



4-34 



2-43 



2-14 



18 V 8 



50-1 



313 



Tate 



•660 



0-299 



4-87 













" 



•700 



0-308 



5-20 









.... 





Ingersoll _ 



•87 



0-203 



6-07 



1-88 



1-89 



36-8 



7~9~-l 



42-3 



it 



1-25 



0-37 



8-88 



1-69 



1-77 



78-6 



152- 



73-4 



. << 



1-75 



0-55 



12-3 



1-27 



1-55 



151- 



260- 



109- 



tt 



2-25 



0-77 



15-4 



1-04 



1-41 



230- 



394- 



164- 



of the optical constants is nearly as precise as that of the 

 methods of measurement used. It is safe to say, however, that 

 no one who has had much experience in this line of work has 

 held such an opinion for long. In fact, experience teaches that 

 it is well nigh impossible to exactly reproduce (even by the 

 same observer) the same condition of the reflecting surface in 

 different samples of the identical material, or even in the 

 same sample at different times. Thus we cannot regard the 

 experimental values of the optical constants of metals as any- 

 thing but rather rough approximations to the specific values 

 characteristic of the substances. Hence any theoretical relation 

 dependent for its numerical evaluation on the absolute values 



* Lummer and Sorge, Ann. Phys., xxxi, p. 325, 19A.0. 



