and Dispersion in certain Metals. 



375 



our method in the case of Fe, Co, and Ni would not subsist 

 when applying it to Au or Ag. In fact we should have had 

 to determine the large deviation from Snellius's law, which 

 doubtless exists, by small differences in the quantities observed. 

 We could hardly have successfully attempted this without 

 refining the observations. 



However, it is possible to foretell the actual shape of the 

 silver and gold curves (fig. 3). They must start from the 

 origin along the same tangent as the dotted curves drawn ; 

 then bend more and more concavely towards the axis of 

 abscissae ; they cannot intersect PQ, as this would mean total 

 reflexion, and must abut normally on QR. Their character 

 therefore is essentially the same as that of our curves obtained 

 for Ni &c. 



II. Dispersion. 

 § 17. The experiments had to be made at the minimum of 

 Table III. 



du Bois. 



Rubens. 



p. 



Deviation a. 



£ 



Deviation «, 



-Lia.. 



P. 



F. 



a. 



Li «. D. 



F. 



G. 



Prism Co. III. 



22 4 



21-8 

 195 



48-2 

 46/2 



40-0 

 41-7 



29-8 

 36-4 



25-1 

 29-0 



23 8 

 24-7 

 216 



51-4 



52-0 



48-8 

 455 



33-4 

 37-7 



20-0 



28-4 



21-2 

 n = 



47-2 

 3-23 



40-8 

 292 



33-1 

 2-56 



271 



2-27 

 Mean 



23-4 



n = 

 n= 



51-7 

 3-21 

 3-22 



47-1 

 3-02 

 2-97 



35-6 



2-52 

 254 



24-2 

 2-04 

 2-16 



Prism Ni II. 



22-2 

 22-7 

 223 



176 

 22-0 



15-7 

 189 



16-8 



15-7 



10-1 

 11-4 



22-3 

 21-8 

 234 



19-7 

 233 



213 

 14-2 



17-6 

 160 



16-4 

 91 



22-4 

 n = 



19-8 

 1-89 



173 



1-77 



16-2 

 1-72 



107 



1-48 

 Mean 



22-5 



71 = 



n= 



215 

 1-96 

 193 



17-8 

 1-79 

 1-78 



16-8 

 1-75 

 1-74 



12-8 

 1-57 

 1-52 



