338 Dr. Seebeck on the unequal Evolution 



In the red 6" 9"' 



One inch below the red 70 



Three lines 7 10 



Difference thirteen lines. 

 Exp. 10. — On another day. The distance the same. 



In the red (without screen) 7" 9''' 



Quarter of an inch below the red 8 5 



Difference eight lines. 



Zjy9. 11.— In the red 7 9^ 



Long remained so. 



Quarter of an inch under the red, it rose in 



■ ) 



few seconds to / 



And at last (where it remained stationary) to 8 10 

 Difference thirteen lines and a half. 



Ejcp. 12.— In the red 7 1 



Below it 7 11 



Difference ten lines. 



The mean of all these experiments would amouHt to ten 

 lines three-eighths. 



Exp. 13. — For the purpose of comparing the effect of the 

 flint-glaSs prisms Nos. 2 and 3, during a perfectly clear sky, 

 SOth May 1808. 



The difference between the station of the thermoscope in 

 the place of experiment, and the maximum of heat immediately 

 below the red, amounted to four inches two lines ; the diffe- 

 rence between the heat in the red and the superior heat close 

 under the red, twice, seven lines; and three times, six Unes. 

 Both prisms produced absolutely the same effects. 



Some experiments were now made with the same prisms, 

 2 and 3, at a distance of four feet (Experiments 14 — 18); and 

 the i-esult was, that the mean difference between the heat in 

 the red and the superior heat beyond the red, for the distance 

 of the thermoscope of four feet, amounted to fourteen lines. 



All other trials made with these prisms gave the same re- 

 sult, the maximum of heat being always foimd beyond the 

 limits of the spectrum. 



I now refer to experiments made with other prisms (Nos. 1, 

 5, and 6) of Bohemian glass ; and first a series of them made 

 on the favourable SOth May 1808, immediately after the 13th 

 experiment mentioned above. (Experiments 19 — 23.) 



These experiments, compared with the 13th, gave the most 

 convincing proof that glasses of different composition and quali- 

 ties alsodiffer in their effects. For in all these experiments (from 

 19 to 22) made with prisms approaching to crown-glass in their 



refraction 



