against, the person. However this may be, it is a most important thing that this very dangerous class of crime should be subject to ready detection. The microscope alone will not aid us much, although we can de tect by its aid places in paper where erasures have beer. made. If any one will take the trouble to examine microscopically the paper on which these words are printed, using quite a low-power object-glass, he will note that its smooth surface altogether disap pears, and that it seems to be as coarse as a blanket This being the case, it will be readily understood that an erasure with a knife, which would be imperceptible to the unaided eye, becomes so exaggerated when viewed with the microscope that there can be no mistake about it. In examining writing by this searching aid to vision, the finest lines appear thick and coarse. It is also possible to ascertain whether an altera tion has been made in a word before the ink first applied has become dry, or whether the amendment has been an afterthought. In the former case, the previously applied ink will more or less amalgamate with and run into the other, as will be clearly seen under the microscope; while in the latter case, each ink-mark will preserve its own unbroken outline. The use of this observa tion in cases of suspected wrong-doing is obvious. Dr. Jeserich shows two photo graphs which illustrate these differences. In the first, a document dated early in Jan uary is marked 1884, — the 4 having been altered into a 5 as soon as written, so as to correct a mistake which most of us make a dozen times or more at the beginning of each new year. In the other picture, the date had been altered fraudulently, and long after the original words had been traced, in order to gain some unworthy advantage. The photographic plates by which these records have been accomplished are the ordinary gelatine plates which are being used in the present day by thousands of amateur workers. By special preparation, these plates can be made to afford evidence
of a far more wonderful kind, and can in certain cases be made to yield a clear image of writing which has been completely cov ered with fresh characters by the hand of the forger. In this way the true and the false are distinctly revealed, together with the peculiarities belonging to each, clearly defined. The word " ordinary " has a special sig nificance to photographers, and is used by them in contradistinction to a color-sensitive (orthochromatic) plate. This second kind of sensitive surface is of comparatively recent date, and the great advantage in its use is, that it renders colors more according to their relative brightness, — just, in fact, as an engraver would express them by dif ferent depths of " tint." These plates are especially useful in photographing colored objects, such as paintings in oil or water color. Dr. Jeserich has, however, pointed out an entirely new use for them, and has shown that they will differentiate between black inks of different composition. The oft-quoted line, " Things are not al ways as they seem," is very true of what we call black ink. It is generally not black, although it assumes that appearance on paper. Taking, for experiment, the black inks made by three different manufacturers, and dropping a little of each into a test-tube half-full of water, the writer found that one was distinctly blue, another red, and the third brown. Each was an excellent writingfluid, and looked as black as night when aplied to paper. Now, Dr. Jeserich prepares his color-sensitive plates in such a way that they will reveal a difference in tone between inks of this description, while an ordinary plate is powerless to do anything of the kind. Among other examples, he shows the photograph of a certain bill of exchange, whereon the date of payment is written April. The drawer of this bill had declared that it was not payable until May; where upon Dr. Jeserich photographed it a second time, with a color-sensitive plate. The new photograph gives a revelation of the true
