as Dr. Seebeck ow the wieqiial Eiiolution 



red, without his having mentioned tliis circumstance. And 

 yet it has been shown by the above experiments that even 

 there the effect on the thermometer is still continued. To 

 seek for any other explanation of this deviation would be use- 

 less, since Mr. L. has not thought proper to give us any de- 

 tails of his experiments. 



M. Wiinsch, who has also appeared as an opponent of 

 Herschel, maintains in the collection of the results of his ex- 

 periments *, that all his prisms gave, quite near the red edge, 

 although outside of it, always the lowest temperature ; that it 

 was stronger in the red, and still more so in the yellow. This 

 assertion, however, is by no means borne out by the experi- 

 ments given by him. He found the maximum of heat in the 

 yellow only, with water, spirits of wine, and oil of turpentine 

 prisms ; and it was different with the glass prisms of which he 

 made use. The first one, stained slightly green, ^ave the 

 greatest heat in the MI redf ; it being the same as with my 

 prisms, Nos. 1, 4, 5, 10, 11, and 12. The second, a prism of 

 a yellowish tint, excited the greatest heat in the glimmering 

 light at the limit of the red J; and a third prism, which was 

 quite colourless, seems to have had the same effect. He men- 

 tions the latter in the same article, p. 202, without givuig, 

 however, any detail of the experiment. These two prisms, 

 therefore, seem to have resembled in effect those of my own, 

 designated by Nos. 6, 7, 8, and 9. Of prisms of flint-glass 

 Mr. W. made no use. We therefore find here no further ex- 

 planation respecting my 7th position ; but the 3rd, 5th, and 

 6th are confirmed by it. 



I can, however, not omit mentioning a deviating observa- 

 tion of Mr. Wunsch's, especially as it may be considered a 

 confirmation of one made before by Rochon. It is, that Mr. W. 

 remarked several times that his yellowish prism excited as 

 great a heat in the orange as on the limit of the red, and that 

 in such case, the heat in the red, lying between those two 

 points, was lower §. This, however, only occurred when Mr. W. 

 made use of a lens of five inches diameter for the purpose of 

 concentratmg the coloured light, but not when he allowed the 

 prismatic orange to fall immediately on the thermometer, as 

 may be seen from the comparison of his 8th and 9th experi- 

 ment with the 1 0th. It would be worth while to investigate 

 whether the difference resulted from the effect of the lens (which 

 is most probable), or from other circumstances. In that case, 



* Mag. der Gesellsch. Naturf. Freunde zu Berlin. 1 Jalirg. 3 /le/f. p. 20.1. 



+ Vide his 1st, 2d, and 3rd Experiment. 



t Vide his 8th, 9th, 10th, 17th. 18th, and 20th Experiment. 



§ Vide his 8th and 9th Experiment. 



however, 



