on Magnetic Rotatory Polarization in Gases. 425 



It has been shown that the luminous rays studied had not 

 in each case the same wave-length, but that their average 

 wave-length could be deduced from the magnetic rotation of 

 the carbon bisulphide. 



As the phenomenon has been exhaustively studied with 

 regard to liquid bodies, such as carbon bisulphide, we can 

 limit ourselves to comparing the relations of the magnetic 

 rotations for the same colours with this body and with the 

 different gases studied. The St.-Gobain glass, which has 

 been made the object of special determinations in this memoir, 

 can also serve for comparison. 



By taking the average of the results obtained with each of 

 the coloured screens employed, the results indicated in the 

 following table were obtained; the unit to which the rotations 

 for each substance were referred was the rotation obtained 

 with the yellow light D, or the rotation deduced from the 

 fourth white image. 



Dispersion of the Planes of Polarization of Kays of different 

 Wave-lengths. 



Bodies. 



Magnetic rotations. 



Carbon bisulphide (liquid) 



St.-Gobain glass 



1 



x 2 



Oxygen..... 



Atmospheric air 



Nitrogen , 



Carbonic acid 



Nitrous oxide , 



Sulphurous acid 



defiant gas , 



Eed. 



Yellow D, 



4th white 



image. 



0-836 

 0-845 



0-850 



0-860 



0-853 

 0-849 



1-000 

 1-000 



1-000 



1000 

 1-000 

 1-000 

 1-000 

 1-000 

 1000 



White. 



1-066 

 1-055 



1-060 



1-066 



Green. 



1-290 

 1-290 



1-250 



1-250 



1-246 

 1197 

 1-256 

 1-235 



Blue. 



1-480 

 1-51 



1-390 



1-39 



1-33 



We see, first of all, that the statements of the rotations for two 

 self-colours are nearly the same for liquids, gases, and solids. 

 Oxygen, to which we shall return later, must be excepted. 

 If the numbers contained in the summary (pp. 422, 423) be 

 compared with those which were obtained by the glasses of 

 the tube, it will be found that the numbers relative to the 

 glasses of the tube are very nearly ten times those obtained 

 for the air, and that in the two tables the same figures are 

 sometimes reproduced for the same colours. I would again 

 refer to the comparison made between the numbers obtained 

 with the different white images. 



These considerations enable us to see that the precision of 



