164 



Professor Forbes on the Refraction 



which, whilst it points out the mode of operating, will exhibit the 

 constancy and considerable magnitude of these effects, amidst 

 the complicated changes of condition to which the heat is sub- 

 jected. The columns marked " corrected," have a small correc- 

 tion applied for the gradual alteration in the quantity of heat 

 reaching the pile, which corrections are interpolated from the 

 successive observations marked (1), (2), (3), &c. which are made 

 under similar circumstances. 



1835. Jan. 16. — Source of Heat. Incandescent Platinum. Pola- 

 rizing Mica Plates E and F. Film of Mica interposed, No. 1. 



Position of 

 Mica plates. 



[E at 0°"| 

 F at 90° 



F at 0° 

 F at 90° 

 F at 0° 

 F at 90° 

 F at0° 

 F at 90° 

 F at 0° 

 F at 90° 

 F at 0° 

 F at 90° 

 FatO 



Principal Section 



of interposed 



Mica, at 



(45° (1) 

 10 



45 

 : 45 



(2) 



{1 



{o 



1 45 



J 45 (S) 



1° 



\° 



145 



/45 (4) 

 \0 



J° 

 I 45 



f 45 (5) 



(0 



J° 



(45 



J 45 (6) 

 \0 



1° 

 \45 



Multiplier. 



14°.8 



12 .0 

 18.0 



15 .3 

 14.8 

 12.6 



16 .6 

 14.2 

 14.1 

 11 .6 

 16.4 

 13.4 



13 .8 

 11 .8 

 16.3 

 13.8 

 13.6 

 11 .2 

 16.1 

 13 .8 

 13.0 

 10.6 

 15 .6 

 13.5 



Total Po- 

 larization. 



6°.0 





4.0 



4.8 





4.5 





4.9 





5.0 



Depolariza- 

 tion. 



+ 2.0 



Total Po- 

 larization 

 Corrected. 



6°.0 



4 .2 



4.9 



4 .5 



5 .0 



5.1 



Depolari- 

 zation 

 Corrected 



2°.75 



2.1 

 2.65 

 2.2 

 2.2 



2 .2 



Mean, 



Ratio. 



100 : 46 



100 : 50 



100 : 54 



100 : 49 



100 : 44 



100 : 43 



100 : 48 



When the analyzing plate F is said to be at 0°, it is parallel 

 to the plate E. When the principal section of the interposed 

 film is at 0°, it is parallel to the plane of incidence at the plate 



