and on the Motion accompanying Heat-conduction. 165 



mirror, than when the two formed a right angle with one another. 

 Hence it follows that the radiant heat is partly polarized, and 

 that, as with incandescent platinum plates, its plane of polariza- 

 tion is perpendicular to the plane of reflection. Starting from 

 the hypothesis that the deflections of the galvanometer are pro- 

 portional to the quantities of heat, the values found give the 

 relation between the polarized and the entire amount of radiated 

 heat. For, assuming that the mirror in both positions reflects 

 only polarized heat, the entire radiated heat is proportional to 

 the sum of the reflected quantities in the two positions of the 

 mirror, and the difference of these quantities is proportional to 

 the polarized portion. 



In the first place, experiments were made in which the polished 

 face of the radiating vessel made of tinned iron-plate sent its 

 heat against the reflecting mirror. In the following Table are 

 contained three series of experimental numbers obtained in this 

 manner. In the first the original observations are given, in 

 order to show how far these agree with the mean values ; in the 

 remainder the mean values alone are given. A polished copper 

 plate was then fastened upon the tin plate, and this again was 

 afterwards replaced by a polished plate of aluminium. The 

 latter was used to decide whether metals of very different speci- 

 fic gravity might show differences in the polarization, and conse- 

 quently in their refractive powers. 



Table I. — Radiating surface : — polished metal. 



Radiating 

 surface. 



Horizontal 

 upwards. 



To the left. 



Horizontal 

 downwards. 



To the right. 



Analyzing 

 mirror. 



Left 



Horizontal 



Right 



Left 



Horizontal 



Right 



Left 



Horizontal 



Right 



Left 



Horizontal 

 Right 



Tinned-iron plate. 



Series of experiments I. II. Ill 



9 



4-5 



8 



3 



5 



4-5 



625 



4 



5-5 



3-25 



5 



4-25 



8-o 



5 



8-5 



375 



5 



5 



6 



4 



6 



3 



4-5 



3-25 



9 



5 



9 



4 



5 



4-25 



6 5 



4 



5-75 



3-5 



5 



3-25 



Mean of 'all k values [with perpendicul 



of reflection 



Mean of all values with parallel 



reflection 



Total heat or sum 



Polarized portion or difference 



Percentage of polarized portion of the entire 

 heat 



ar planes "\ 

 planes ofl 



mean. 

 875 

 4-8 

 8-5 

 3-5 

 5 



4-5 

 6-25 

 4 



575 

 325 

 4-8 

 3-6 



6-46 



3-96 



10-42 

 I 2-50 



24 



mean, 

 7-4 

 37 

 725 



3-4 

 21 



275 



5-2 



4-5 



4-6 



2-3 



5-57 



mean, 

 9 



6-5 

 9-2 

 3 



5-5 

 3-6 

 5-2 

 3 

 6 



2-6 

 5 

 2-8 



6-65 



3-07 ' 358 



8-64 10-23 



2-50 | 307 



29 130 



Cop- 

 per. 



mean. 

 9-2 

 6-8 

 87 

 2-8 

 31 

 26 

 31 

 21 

 375 

 26 

 31 

 275 



5-16 



3-27 



8-43 

 1-89 



22-4 



Aluminium. 



mean. 

 73 

 4 



7-2 

 1-6 

 3-3 

 21 

 4-5 

 2-8 

 4-9 

 2-8 

 4 

 31 



5-2 



27 



7-9 

 2-3 



29 



II. 



mean. 

 7-6 

 41 

 6-6 

 2-25 

 4-5 

 2-9 

 4-3 

 27 

 4-6 

 3-2 

 3-9 

 2-8 



5-3 



8-3 

 2-3 



28 



