in the Infra-red Region of the Spectrum. 741 



With the linear displacements known to y^oo" mm - ^ ,no fourth 

 figure might have been obtained. However, the above men- 

 tioned lack of symmetry in the curves made it uncertain. 

 The following table gives the results I obtained : — 



Table I. 



\ in fi. 



Ad in mm. 



Ap' in 

 mm. Hg 



Temp, 

 in °0. 



«o— 1. 



n — 1 at 

 and 760 mm. 







at 0° O. 





Absolute value. 



0-5894 Na 



30334 



1411-5 



18°-27 



0000439 6 



00004508 



0-8 



3-061 



14331 



18° -25 



436 9 



448 x 



1-0 



3 018 



1433- 1 



18°-15 



430 8 



44l 6 



20 



2-965 



1433- 1 



18°-10 



423 



434 



30 



2-848 



14331 



18°-15 



406, 



417; 



4-0 



1-982 



14331 



18°-15 



279 9 



29l 2 



5-0 



3-642 



14331 



18°-20 



519, 



53J 



67 



3-366 



1433-1 



18°-20 



480. 



491 6 



8-7 



3-135 



1433- 1 



18°-20 



447 4 



458 G 



110 



3-012 



14331 



l8°-20 



429 9 



441 x 



0-5894 Na 



3-0551 



1418-6 



1 8° -35 



440 7 



1 0-0004508 



0-5394 Na 



30690 



14231 



18°-20 



441. 



0-8 



3042 



1427-5 



I7°33 



434 



444 5 



10 



3-018 



14275 



17°37 



431. 



441, 



20 



2-961 



14275 



17°-35 



423 



432 9 



30 



2-865 



1427-5 



17°-40 



409 4 



419 3 



40 



1-938 



14275 



17°-45 



276 9 



286 8 



50 



3-655 



1427-5 



17° -45 



522 



532 2 



6-7 



3-260 



1427-5 



17°-52 



466 



475 9 



8-7 



3131 



1427-5 



17°-52 



447 6 



457 5 



110 



3-031 



1427 5 



17°-55 



443 3 



453 5 2 



1319 



2-730 



1427-5 



17°-60 



390 5 



400, 



Table II., below, contains the average of various values of 

 ?i — 1 corrected by means of the known absolute value of 

 ti — 1 for sodium. This value is taken as the average of those 

 given by Ketteler, Mascart, Chappuis and Riviere, Perreau, 

 and Walker. 



Table II. 



\ in /u. 



Average value. 



Observer. 



0-5894 Na 



0-0004508 [ 



Avernge from values 

 of Ketteler, Mascart, &c. 



0-8 



446, 



Statescu. 



10 



441 





20 



433 fl 





30 



418, 





40 



2S9 5 





50 



531 





6-7 



483, 





6-7094 



48038 



J. Koch. 



8-7 



458 t 



Statescu. 



8-6784 



45792 



J. Koch. 



110 



447o 



Statescu. 



13-19 



400 4 



» 



