32<3 PROCEEDINGS OF THE AMERICAN ACADEMY 



It now becomes my agi'eeable duty to announce the fact tliat, after a 

 careful review of the meritorious services of Pi'ofessor Draper iu this 

 great field of inquiry, the committee having the subject iu their charge 

 have, for reasons given by them, recommended through their Chair- 

 man, that the medals prescribed in the deed of trust should be presented 

 to him as having fully deserved them. It falls to my lot only to re- 

 capitulate in brief some of these reasons. 



In 1840 Dr. Draper inde[)endently discovered the peculiar pheno- 

 mena commonly known as Moser's images, which are formed when a 

 medal or coin is placed upon a polished surface of glass or metal. 

 These images remain, as it were, latent, until a vapor is allowed to 

 condense upon the surface, when the image is developed and becomes 

 visible. 



At a later period he devised the method of measuring the intensity 

 of the chemical action of light, afterwards perfected and employed by 

 Bunsen and Roscoe in their elaborate investigations. This method 

 consists in exposing to the source of liglit a mixture of equal volumes 

 of chlorine and hydrogen gases. Combination takes place more or 

 less rapidly, and the intensity of the chemical action of the light is 

 measured by the diminution in volume. No other known method 

 comjiares with this in accuracy, and most valuable results have beea 

 obtained by its use. 



In an elaborate investigation, published in 1847, Dr. Draper estab- 

 lished experimentally the following important facts : — 



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 Fahrenheit degrees. 



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° Fahrenheit, 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 tem- 

 perature rises. 



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

 temperature is higher, is taking place, there is an increase iu the inten- 

 sity of those already existing. 



Thirteen years afterward, Kirchhofi" published his celebrated memoir 

 on the relations between the coefficients of emission and absorption of 



