294 [Dec. 1, 



' Transactions of the Royal Society of Edinburgh,' Mr. Balfour 

 Stewart has made the requisite extension of Prevost's theory in the 

 case of radiant heat, deducing important consequences which he has 

 verified by experiment. The transition was natural from radiant 

 heat to light, and was made by Mr. Stewart himself. The paper 

 containing this extension of the theory, and the experiments by 

 which he had verified it, was published in the ' Proceedings of the 

 Royal Society' for March 15, 1860, and accordingly only a very 

 short time after Professor Kirchhoff announced to the Berlin Academy 

 his discovery of inversion. Mr. Stewart, however, did not occupy 

 himself with the emission of rays of definite refrangibility, his expe- 

 riments having been chiefly made on heated coloured glasses. 



The great number of the dark lines in the solar spectrum renders 

 necessary a very exact determination of the places of dark and bright 

 lines, lest an accidental juxtaposition should be mistaken for coin- 

 cidence. To prosecute his researches with success, Professor Kirch- 

 hoff found it necessary to prepare a map of the solar spectrum com- 

 bining largeness of scale with exactness to an extent not to be found 

 in any published map ; and to this laborious undertaking he vigor- 

 ously applied himself. The result may be judged, of by the admirable 

 map of a portion of the spectrum published in the ' Transactions of 

 the Berlin Academy ;' but, unfortunately, the very zeal with which 

 Professor Kirchhoff prosecuted his observations threw an obstacle 

 in the way of his progress. The constant strain brought on a weak- 

 ness of the eyes, which obliged him to suspend his observations for 

 a time. It is understood, however, that the work is progressing, as 

 other observers are engaged in taking the observations which he 

 himself could not prudently continue. 



PROFESSOR MILLER, 



In delivering to your care as our Foreign Secretary this Medal, to 

 be transmitted to Professor Kirchhoff, we will ask you to accompany 

 this testimony of our high esteem by the expression of our sympa- 

 thy in the cause which has temporarily interrupted the excessive 

 devotion with which he has pursued his valuable researches, and 

 of our hope that he will not permit himself to be tempted person- 

 ally to resume his observations until his eyes shall have perfectly 

 recovered. 





