[ 330 ] 



LIV. On the unequal Evolution of Heat in the Prismatic Spec- 

 trum. By Dr. T. J. Seebeck *. 



T ANDRIANIf, one of the first who made expenments 

 -*-^ on the heating power of tlie coloured light given by 

 the prism, found the greatest heat in the yellow rays. But 

 Rochon:f places the maximum of heat between the yellow and 

 the red, in a point which he calls sometimes orange, sometimes 

 jaime orange. Senebier§ gives as the result of many experi- 

 ments, that the red light was always warmer than the violet, 

 and the yellow sometimes warmer than the red ; and in the 

 examples given by him as a confirmation, and which he says 

 are the mean of many experiments, the yellow light is found 

 to be the warmest. Herschel's experiments || differ from all 

 the rest. He found the strongest heat neither in the yellow 



• From Schweigger's Journal, Band x. p. 129. This paper was read be- 

 fore the Royal Academy of Sciences of Berlin, March 13, 1819, but has 

 only recently appeared in their Transactions. The German editor give? 

 the following statement of his reasons for reprinting it : 



" Although it may be supposed that extracts from the memoirs of literary 

 societies, even those ofGermany, may be desirable for persons who have no 

 access to larger libraries, I have nevertheless been very sparing of them, 

 unless the authors themselves have had the kindness either to send me co- 

 pies of their productions, or, what is always most desirable, have made such 

 extracts themselves. In the present instance it is intended to give merely 

 the results of the experiments, and to mention the experiments themselves 

 only so far as may seem necessary to understand their nature. The special 

 cause, however, for publishing this extract now, is an announcement con- 

 tained in the Annals of Philosophy for Nov. 1823, p. 394, relative to a 

 work on this subject intended to be published by Mr. Powell ; and from 

 which it would seem that Mr. P. has overlooked several essential points, 

 which the reader will find in Seebeck's memoir. We will, however, wait 

 for Mr. P.'s publication, and extract from it whatever may be required in 

 addition to the present." 



The series of papers on the subject by Mr. B. Powell will be found in 

 the Annals of Philosophy, N. S. vols. vii. viii. and ix. ; and one in the Phi- 

 losophical Transactions for 1825, part i., or Phil. Mag. vol. Ixv. p. 437. An 

 extract from Dr. Seebeck's paper, being the only notice of it which has yet 

 appeared in this country, was given in the Annals of Philosophy for Sep- 

 tember 1824, and commented upon by Mr. Powell in a subsequent number 

 of the same work. 



f S. Volta, Lettere suW Aria infiammahile nativa delle paludi. Milano 

 1777, P- 13^- flifi experiments of Landriani are said to be contained in the 

 Scelta d'Opuscoli interessanti, vol. xiii., which I have not been able to pro- 



t ' Recucil des Mcmoircs siir la Mecanique et la Physique, p. 348—355. 

 Paris 1783. Rochon's experiments were made during the summer months 



§ Fhisikalisch-chemuche Abhandlungen uber den Einfluss des Sonnenlichtes 

 aufalle drei Reichc dcr Natur. vol. ii. p. 37. Leipz. 1785. 

 li Phil. Trans, for 1800, p. 255-326, and p. 437—538. 



nor 



