MEMOIR V.] INTERFERENCE OF RADIATIONS. 



MEMOIR V. /t > 



ON THE NEGATIVE OK PKOTECTING RAYS OF ' THENS^N. 



From the Philosophical Magazine, Feb., 1847. 



CONTENTS: Original discovery of protecting radiations. Case of a 

 daguerreotype plate. Spectrum-photographs made in Virginia. Pro- 

 tecting action of the less refrangible rays. Protecting action of the 

 extreme violet. Variations of the protecting action. Spectrum of 

 darkness and spectrum of daylight. Interference of rays of different 

 colors. Action of waves of red, yellow, and violet light with wave- 

 lengths 2, 1^, 1. Use of the diffraction spectrum. 



IN a letter published in the Philosophical Magazine 

 Nov., 1842, I had occasion to make some incidental re- 

 marks respecting a class of rays existing in the sunlight 

 which have the quality of exerting a negative or antag- 

 onizing action upon those engaged in producing daguerre- 

 otype results. 



In October last, MM. Foucault and Fizeau having 

 made a communication to the French Academy of 

 Sciences to a similar effect, and M. Edmond Becquerel, 

 in criticising their results, having referred to me as the 

 original author of the fact, I may on this occasion be 

 excused for offering a few observations on this, which 

 perhaps is destined to become one of the most important 

 phenomena in relation to the chemical action of the sun- 

 light. 



That the opposite ends of the solar spectrum possess 

 opposite qualities is an idea which has been floating 

 among chemists for many years. The first distinct 

 statement in relation to it with which I am acquainted 

 occurs in a work published by Mr. B.Wilson, the second 



