PREFACE ΤΟ SECOND EDITION. all who practise it to agency by which their The chemistry of the THE Constantly increasing interest in the beautiful Art of Photography, has naturally led desire some knowledge of the pictorial results are produced. solar radiations, or, as it has been appropriately termed, Actino-chemistry, is essentially a new science. The breaking up of strong chemical combinations by a power so subtile as that of the sunbeam, is amongst the most striking of the facts which claim the attention of the natural philosopher. While the physical and chemical phenomena of the solar radiations require for their investigation the aid of all the refinements of modern science. For the purpose of placing in the hands of all who are interested in this science, a clear and satisfactory record of the progress which has been made since the publication of the First Edition of these "Researches," it has been found advisable to entirely recast the work. More than two-thirds of it has therefore been re-written, and the remaining third materially modified. The former Edition was spoken of by some reviewers as a compilation. Since the rewards to the original investigator are but few, I feel it necessary to claim for my labours a higher position. Before the publication of either of the Photographic processes of M. Daguerre or of Mr. Fox Talbot, while yet there were but vague rumours of the production of pictures by Solar Light, the experiments which these "Researches" record were commenced, and they have been continued almost without intermission to the present time. Many of the Photographic processes described were the reward of my experiments. The analyses of the solar beam, determining the relation between the Light and the chemical power of the solar rays are almost entirely original. The investigations on the influence of Light on Germination and the Growth of Plants, with the practical applications which have been made of my discoveries, I can refer to with satisfaction.* I have used the labours of other men no further than they were necessary to illustrate the subject under consideration, and each investigator will, it is hoped, find his labours recorded with careful truth. This Edition of the Researches on Light, whatever may be its value, is the result of thousands of experiments, made at no small cost, and with a large expenditure of thought. I have aimed at the elucidation of an obscure subject; I have endeavoured to keep my mind free of all pre-conceived notions, and to read my experimental results by the illumination they afforded. It is exceedingly probable my interpretations may not be always correct, but my judgment has been founded on a most careful study of all the phenomena observed. * See Appendix, No. III., "On the Use of Blue Glass in accelerating Germination;" and No. IV., "On the Glass in the Palm House at the Royal Botanical Gardens at Kew." PREFACE TO SECOND EDITION. vii In submitting this Volume to the public, I regret having been compelled to say thus much of myself and my labours; but the ungenerous attacks of those with whom I have ventured to differ in opinion have compelled me to the painful task. Truth is the end we seek; and I now venture to commit these few endeavours towards its advancement to the judgment of the world, premising that this volume probably contains the record of labours, which may not be for some time renewed, my duties directing my industry into another and a sterner field of investigation. ROBERT HUNT. London, June 14. 1854. |