THE PHOTOGRAPHIC plate is much more valuable than the human eye, in that it records what it sees. Effects upon it are cumulative; if something is too faint to be seen by the eye we may look at it steadily for hours without results, whereas the longer the sensitive plate is exposed, the stronger becomes the image, until finally it reaches visibility. This property is valuable from a detective standpoint.
At one of the public libraries it was discovered that a copper engraving had been abstracted. The thief had, however, omitted to remove the protecting tissue-paper cover. All efforts, aided by the context, to recall the character of the picture, proved fruitless, and the only resource left open was to endeavor to reconstruct by photographic means the vanished picture from any impression which it might have left upon the tissue-paper cover. This task was accomplished with complete success by photographing through a blue filter and re-enforcing the contrasts by the successive perforation of positive and negative copies. This resort was rendered possible through the fact that the grease of the printers' ink had been partially absorbed by the tissue-paper, and had, by oxidation, imparted to the same a slight yellow coloration quite invisible to the eye. The engraving was later discovered in the thief's possession.
The examination of a drowned woman by photography disclosed distinct evidence of strangulation, marks which were absolutely invisible to the naked eye. On the basis of this evidence it was subsequently established that the drowned person had been thrown into the water after a previous struggle. — "Tracking Criminals by Camera," THE LITERARY DIGEST, November 4, 1911.In case you don't recognize the phrase in the title of this article, it was uttered by none other than that stalwart minion of the law, Deputy Barney Fife.
Category: Detective fiction