LUNI

CHAPTER I

EARLY RESEARCHES ON THE CHEMICAL ACTION OF THE SOLARRAYS.

Ir is instructive to trace the progress of a discovery, from thefirst indication of the truth, to the period of its full development,and its application to purposes of ornament or utility. Theprogress of discovery is ordinarily a slow process, and it oftenhappens that a great fact is allowed to lie dormant for years, orfor ages, which, when eventually revived, is found to render afine interpretation of some of Nature ’s harmonious phenomena,and to minister to the wants or the pleasures of existence.Photography is peculiarly illustrative of this position.

The philosophers of antiquity appear to have had their atten-tion excited by many of the more striking characters of light.Yet we have no account of their having observed: any of its che-

ing their colour in some cases, and discharging it in others—must have been of every-day occurrence. The only facts whichthey have recorded are, that some precious stones, particularlythe amethyst and the opal, lost their sparkle by prolongedexposure to the rays of the sun.