168 REFBANGIBILITY OF 



The first fact recorded upon this point was, that horn 

 silver blackened when exposed to the light. Without 

 doubt many anxious thoughts were given by these 

 alchemists to that fact. Here was, as it appeared, a 

 mixing up of light and matter, and behold the 

 striking change ! It was, a. step towards the realization 

 of their dreams. Alas! poor visionaries! in pursuing 

 an iideality they lost the reality which was within their 

 grasp. 



Truths come slowly upon man, and long it is before 

 these angel visits are acknowledged by humanity. The 

 world clings to its errors, and avoids the truth, lest its 

 light should betray their miserable follies. 



At length a man of genius announced that " No sub- 

 stance can be exposed to the sun's rays without 'ander- 

 (jQing a chemical change-" but his words fell idly upon the 

 ear. His friends looked upon his light-produced pictures 

 as singular; they preserved them in their cabinets of 

 curiosities ; but the truths which he enunciated were 

 soon forgotten. Howbeit his words were : recorded, and 

 it is due to the solitary experimentalist of Chalons on 

 the Saone, to couple the name of Niepce with the dis- 

 covery of a fact which is scarcely second to the develop- 

 ment of the great law of universal gravitation.* But 

 an examination awaits us, which, for its novelty, has 

 more charms than most branches of science, and which, 

 for the extensive views it opens to the inquirer, has an 

 interest in nowise inferior to any other physical investi- 

 gation. 



The prismatic spectrum affords us the means of ex- 

 amining the conditions of the solar rays with great 



Speculum Mundi, or a Glass representing the face of the World. 

 Cambridge, 1648. 



* Daguerre's Eeport to the Academy of Sciences : La Daguer- 

 reotype Historique, et description des precedes du Daguerreotype et 

 du Diorama (Paris, 1831)) ; particularly the description of Helio- 

 yraphy, by M. Niepce. See also the letters by Niepce, published 

 for the first time in Researches on Light. 



