A Manual Of Photography

6 HISTORY OF PHOTOGRAPHY. states, that M. Charles never disclosed any fact connected with his hypothetical discovery, and that he left no evidence behind him of ever being in possession of such a secret process : we may therefore fairly infer that this is a vain boast. In addition to the interesting facts already mentioned, it will be instructive to add a few particulars of other inquiries pursued about the same time on various phenomena connecting themselves with the solar radiations. Although these do not bear directly on Photography, they stand in very close relation with it, and will serve possibly to indicate lines of research which have not been fully followed out. Desmortiers in 1801 published a paper in Gilbert’s Annals, entitled “ Recherches sur la Decoloration spontanée du Bleu de Prusse, ” subsequently translated into Nicholson’s Journal, in which he has mentioned the influences of the solar rays in producing the change. Böckman about the same time observed that the two ends of the spectrum acted differently on phos- phorus ; and Dr. Wollaston, examining the chemical action of the rays of the spectrum, arrived at nearly the same results as Ritter. He states, “This and other effects usually attributed to light are not in fact owing to any of the rays usually perceived.” Attention having been directed by Dr. Priestley in 1779 to the influence of light on plants, numerous inquirers were started on this track, and the valuable researches of Senebier, Ingenhousz, De Candolle, Saussure and Ritter, were the result; Saussure inferring from his experiments that the blue rays were most active in producing the decomposition of carbonic acid by the leaves. These are already too well known to require any- thing beyond this incidental notice ; but in 1801 Labillardière communicated to the Philomathic Society his discovery that light was necessary to the development of pores in plants, and subsequently, we find Victor Michellotti of Turin, in a paper, “Experiments and Observations on the Vitality and Life of Germs,” stating that light has a decided action on those germs whicli are exposed to it, that this action is prejudicial to them, and it manifests its action by retarding their expansion if the light be weak, or a reflected light ; or by the total extinction of their life, if it be very intense, as that which comes directly from the sun.” IM. Macaire Prinsep again states, "that sheltering leaves from the action of light prevents their change of colour in the autumn; that if the entire leaf was placed in the dark, it fell off green ; if only a part, the rest of the parenchyma changed colour, and the covered portion retained its original colour.”