" Law " in Physical Optics. 343 



column 4 gives the ratio of the two indices, which are slightly 

 corrected in column 5. This is done by calculating from 

 columns 2 and 3 the average change in the index per degree, 

 as shown in column 6. The figure thus obtained is used to 

 calculate the change of index for 80° exactly, which means 

 an alteration of only a degree or two for most substances. 

 The ratio in column 5 is calculated then for a common interval 

 of 80°, and will be somewhat nearer the truth than the un- 

 corrected ratio in column 4. 



Column 7 gives the exponent of pu in the statement 



fi* a ;=- where T is the absolute temperature. It therefore 



equals l°g7fr^~ log— . 



The ratio - 1 is about 1"03, so that the different powers of 

 it do not vary so much. 



Substance. 



Heptane 



»> 



Methylene Iodide 



)> 



Toluene 



j> • 



Phenyl Chloride 



j> 



Acetyl -acetone , 



>> ■ 



Methyl-acetyl-acetone 



>j 

 Ethyl -acetyl- acetone. . , 



,, 

 Phenyl Bromide , 



>j 



Phenyl Iodide 



>> 



Aniline 



» 



Dimethylaniline 



>> 



Ethyl- acetone-oxalate 



>» ' 



Ethyl-diaceto-acetate 



,, ... 

 Ethyl Cinnamate , 



j> 



Octyl Iodide 



>i 



Thymol 



>> 



Cinnamic Alcohol 



Temp. 



12 



89 



8 

 87 

 10-7 

 90 



96 

 89-2 

 11 

 99-3 



8-34 

 99-2 

 15-4 

 100-3 



4-2 

 89-2 



8 

 88 

 11-2 

 90-1 



8 



89-7 

 17 

 100 

 17-6 

 99-8 

 12-9 

 91-1 

 14-5 

 88-5 



24 

 77-3 



24-8 

 77-3 



3922 



35197 



74935 



69500 



5028 



45673 



53103 



48731 



44493 



39634 



4421 



39526 



44066 



3952 



56845 



52235 



62755 



58301 



5912 



5487 



5583 



51704 



46503 



4263 



4573 



4193 



5479 



5108 



4922 



4579 



5145 

 4919 

 5731 

 5494 



1*2 



1-0297 

 1-0321 

 1-0316 

 10293 

 1-0349 

 1-0334 

 1-0324 

 10303 

 1-0279 

 1-0274 

 10270 

 10272 

 10270 

 10253 

 10236 



1-0154 

 10153 



corrected 



•0317 

 0325 

 •0318 

 •0295 

 •0314 

 •0295 

 •0307 

 •0285 

 •0279 

 •0278 

 0265 

 •0262 

 •0261 

 •0259 

 •0254 



10154 

 10153 



^i r*2 



000522 

 •000671 

 •000576 

 •000546 

 •000552 

 •000514 

 •000535 

 •000543 

 •000557 

 •000538 

 000510 

 •000536 

 •000463 

 •000476 

 •000463 



•000427 

 •000447 



x = 





lcg^a-i-log^- 1 . 

 14 



8'1 



8-0 



8-05 



8-84 



7-92 



8-49 



8-0 



9-46 



9-17 



923 



9-6 



9-35 



9-29 



993 



9-99 



10-7 

 10-6 



