To the sum total of human knowledge no department of science has contributed more than that of optics. With the telescope man has climbed into the limitless space of the heavens, and ascertained the infinite vastness of the universe. The flaming sun which warms and vitalizes the world, is found more than ninety millions of miles away. The nearest fixed stars visible to the naked eye are more than 200,000 times the distance of the sun, and their light, traveling at the rate of 190,000 miles a second, requires more than three years to reach us. Although so far away, their size, distance, and constitution have been ascertained, and their movements are scheduled with such accuracy that the going and coming thereof are brought to the exactness of a railroad time table. The astronomer predicts an eclipse, and on the minute the spheres swing into line, verifying, beyond all doubt, the correctness of the laws predicated for their movements. The wonders of the telescope, the microscope, and the spectroscope are, however, but suggestions of what we may still expect, for science abundantly teaches that the eye may yet see what to the eye is now invisible, and that light exists in what may now seem darkness. No man may say with certainty what thought was uppermost in Goethe’s mind when, grappling in the final struggle with the King of Terrors, he exclaimed “Mehr licht!” It may be that it was but the wish to dispel the gathering gloom of his dimming senses, or perchance the unfolding of an illuminated vision of a brighter threshold, but certain it is that no words so voice the aspirations of an enlightened humanity as that one cry of “More light!” CHAPTER XXIV. PHOTOGRAPHY. EXPERIMENTS OF WEDGEWOOD AND DAVY--NIÉPCE’S HELIOGRAPHY--DAGUERRE AND THE DAGUERREOTYPE--FOX TALBOT MAKES FIRST PROOFS FROM NEGATIVES--SIR JOHN HERSCHEL INTRODUCES GLASS PLATES--THE COLLODION PROCESS--SILVER AND CARBON PRINTS--AMBROTYPES--EMULSIONS--DRY PLATES--THE KODAK CAMERA--THE PLATINOTYPE--PHOTOGRAPHY IN COLORS-- PANORAMA CAMERAS--PHOTO-ENGRAVING AND PHOTO-LITHOGRAPHY--HALF TONE ENGRAVING. “Art’s proudest triumph is to imitate nature.”