CONTENTS. XV 



CHAPTER XI. 



ON THE PROCESS OP DAGUERREOTYPE, AND ITS APPLICATION TO TAKING PORTRAITS FROM THE LIFE. 



Daguerreotype Portraits from the Life first taken. Spectral Images. Preservation of the Sensitive 

 Plate increases the Sensitiveness. Modifications in the Daguerreotype Process. -Moonlight, Ar- 

 tificial Light, and Drummond's Light, are all Active. Description of the original Process of 

 taking Portraits from the Life Page 136 



CHAPTER XII. 



ON SOME ANALOGIES BETWEEN THE PHENOMENA OF THE CHEMICAL RAYS AND THOSE OF RADIANT HEAT. 



Object of the Memoir. On the Daguerreotype Process. Chemical Constitution of Daguerreotype 

 Pictures. Spectral Images. Film of Iodide torn off Mechanically. Iodine is not evolved, but 

 corrodes the Plate. The Chemical Rays are absorbed. The Photographic Effects are transient. 

 The Chemical Rays are not conducted. They become Latent. Optical Qualities control Chem- 

 ical Action. The Active Rays are absorbed, and the Complimentary reflected. Relation of Op- 

 tical Forces and Chemical Affinities . ... . . . . . . 144 



Note added to the preceding Chapter. 



ON CERTAIN SPECTRAL APPEARANCES, AND ON THE DISCOVERY OF LATENT LIGHT . 156 



CHAPTER XIII. 



ON A NEW IMPONDERABLE SUBSTANCE, AND ON A CLASS OF CHEMICAL RAYS ANALOGOUS TO THE RAYS 



OF DARK HEAT. 



Analogies between the Chemical Rays and Heat.- New Nomenclature proposed. Tithonic Rays. 

 Independence of Tithonic Rays and Light. Independence of Tithonic Rays and Heat. Dark 

 Tithonic Rays . . . . . I . . . . . . . '. \ .-' . 158 



Note added to the preceding Chapter. 



ON THE RAPID DETITHONIZING POWER OF CERTAIN GASES AND VAPOURS, AND ON AN INSTANTANEOUS 



MEANS OF PRODUCING SPECTRAL APPEARANCES. .... 165 



CHAPTER XIV. 



ON A NEW SYSTEM OF INACTIVE TITHONOGRAPHIC SPACES IN THE SOLAR SPECTRUM ANALOGOUS TO THE 

 FIXED LINES OF FRAUNHOFER, AND ON THE TITHONOTYPE. 



Mode of Producing the fixed Lines. Description of them. Difficulty of obtaining them in the Yel- 

 low and Green. 



Daguerreotypes are dotted Surfaces. Mode of copying them by the Tithonotype. Polarized Struc- 

 ture of the Daguerreotype Film . . . . . . . . . . .169 



CHAPTER XV. 







ON THE DECOMPOSITION OF CARBONIC ACID GAS AND THE ALKALINE CARBONATES BY THE LIGHT OF 



THE SUN, AND ON THE TITHONOTYPF. 



Dr. Daubeny's Experiments. Importance of the Subject. Decomposition in the Prismatic Spectrum. 

 Decomposition under Absorbent Media. Decomposition is due to Light. Disturbing Causes. 

 Analysis of Gas evolved. Decomposition of Saline Bodies. Production of Nitrogen. Disap- 

 pearance of Oxygen. Character of Chlorophyl. 



Tithonotypes in Copper. Detithonizing Power of Gases 175 



