44'6 Dr. Seebeck on the u?iequal Evolution 



Thus the difference in the statements of the philosophers 

 mentioned at tlie beginning of this essay, respecting tlie place 

 of the greatest heat, will also be more easily imderstood. Those 

 who did not make use of similar instruments could not obtain 

 similar results. There have, however, been instances in which 

 prisms of the same kind were used by diflFerent observers, and 

 still they pretended that their results were different. We will 

 now try whether by a closer examination and comparison of 

 the experiments made by those natural philosophers, — to which 

 we may also add those made subsequently by Wiiusch, Bei'ard, 

 and Ruhland, — a reconciliation of the existing contradictions 

 may not be obtained. 



But before doing so I will class together the chief results 

 of my experiments. 



1. An increase of heat is effected in all spectrums, which is 

 always least at the extreme limit of the violet. 



2. Thence it increases progressively through the blue, green, 

 and yellow, to the red ; and 



3. Attains with some prisms its maximum in the yellow, 

 viz. in the water-prism (Experiment 39) ; and, according to 

 M. Wiinsch's experiments, also with prisms filled with spirits 

 of wine and oil of turpentine. 



4-. Some liquids, viz. a perfectly clear solution of sal am- 

 moniac and corrosive sublimate, and likewise concenti'ated and 

 colourless sulphuric acid, had the maximum of heat between 

 the yellow and the red, — in the orange. (Experiments 40 — 

 43.) 



5. Prisms of ci'own-glass and common white glass have the 

 greatest heat in tlie full red. (Experiments 1 — 5, 20, 21, 



&c.) 



6. With some prisms the maximum of heat falls in the li- 

 mit of the red, and these seem to contain lead. (Vide Experi- 

 ments 24—30.) 



7. Prisms of fluit-glass have the maximum of heat beyond 

 the red when the bulb of tixe thermometer stands outside the 

 well defined spectrum. (Experiments 6 — 18, and 31.) 



8. The heat regularly decreases beyond the red, and with 

 all prisms without exception ; evolution of heat is yet found a 

 few inches below the limit of the red. (Experiments 2, 3, 7, 

 &c.) 



In the two first positions, all observers agree ; but not so 

 in the others. Many have even thought it superfluous to men- 

 tion of what prisms they made use, no doubt thinking that 

 one spectrum would be like the other in eftect. Thus Her- 

 schel has not said of what species of glass the prism consisted 

 with which he made the discovery of the maximum of heat 



bevond 



