APPENDIX. 465 



" 1. All solid substances, and probably liquids, become incandescent at 

 the same temperature. 



"2. The thermometric point at which substances become red-hot is 

 about 977 Fahr. 



" 3. The spectrum of an incandescent solid is continuous ; it contains 

 neither bright nor dark fixed lines. 



"4. From common temperatures nearly up to 977 Fahr., the rays 

 emitted by a solid are invisible. At that temperature they are red, and 

 the heat of the incandescing body being made continuously to increase, 

 other rays are added, increasing in refrangibility as the temperature 

 rises. 



" 5. While the addition of rays, so much the more refrangible as the 

 temperature is higher, is taking place, there is an increase in the in- 

 tensity of those already existing. Thirteen years afterwards Kirchhoff 

 published his celebrated memoir on the relations between the coeffi- 

 cients of emission and absorption of bodies for light and heat, in which 

 he established mathematically the same facts, and announced them as 

 new. 



" 6. Dr. Draper claims, and we believe with justice, to have been the 

 first to apply the daguerreotype process to taking portraits. 



" 7. Dr. Draper applied ruled glasses and specula to produce spectra 

 for the study of the chemical action of light. The employment of 

 ruled metallic specula for this purpose enabled him to avoid the ab- 

 sorbent action of glass and other transparent media, as well as to es- 

 tablish the points of maximum and minimum intensity with reference to 

 portions of the spectrum defined by their wave-lengths. He obtained 

 also the advantage of employing a normal spectrum in place of one 

 which is abnormally condensed at one end and expanded at the other. 



" 8. We owe to him valuable and original researches on the nature of 

 the rays absorbed in the growth of plants in sunlight. These researches 

 prove that the maximum action is produced by the yellow rays, and they 

 have been fully confirmed by more recent investigations. 



" 9. We owe to him, further, an elaborate discussion of the chemical 

 action of light, supported in a great measure by his own experiments, 

 and proving conclusively, and, as we believe, for the first time, that rays 

 of all wave-lengths are capable of producing chemical changes, and that 

 too little account has hitherto been taken of the nature of the substance 

 in which the decomposition is produced. 



" 10. Finally, Dr. Draper has recently published researches on the dis- 

 tribution of heat in the spectrum, which are of the highest interest, and 

 which have largely contributed to the advancement of our knowledge 

 of the subject of radiant energy. 



G G 



