Thus in Fig. B the words "in full to date" were added to the receipt after the signature had been put, and it will be noticed in the enlargement of the cross stroke of the "t" in "date" and the top of the capital "C" in the signature (Fig. C), that the alleged older writing comes uppermost. The point at issue in this dispute was whether the receipt referred to a whole sum or only to a payment on account. The writer in the course of his experience has seen many similar fraudulent alterations, but has never met with a case like that described by Mr. Osborn, where the perforations which are in common use as a means of preventing fraud had been carefully filled in, and new perforations made. Fig. D shows that a fraud of this kind may be detected with certainty by the aid of the microscope, the edges of the original perforations appearing as rings of a lighter hue. [Illustration: ALTERED NUMBER] [Illustration: ALTERED PERFORATION Detection of Forgery by means of the Camera and the Microscope _By kind permission of "Knowledge"_] The subsequent addition of writing to a document was in one instance detected by the fact that the paper had been folded before the later writing was introduced, and in the crease thus formed the sizing on the surface of the paper had become worn, leaving the fibres more porous. Here the ink had shown a tendency to become diffused, and the blurred edges of the lines thus produced were very manifest. Even where paper has been so completely charred that no signs of writing remain visible, it is frequently possible to render the characters visible once more by continuing the incineration until only a white structure of ash remains. When the writing was originally in ink the characters will usually appear in reddish-brown marks (due to the iron in the ink) upon the white background of ash. In the case of inks that do not contain iron, or when the writing was in carbon or aniline typing ink, this method of incineration will prove unsuccessful. Writing that has been done with an ordinary lead pencil can usually be rendered visible by carefully regulating the heat during the incineration, so as not to burn away the graphite. Marks done with a red pencil are, as a rule, burned away with the paper, but blue pencil marks usually persist owing to the presence of an iron compound in the pigment. In the case of printing inks it is rarely possible to render the characters visible again, except when, as in blue printing ink, some iron pigment was present. The limits of this method of reading writing upon charred paper have recently been investigated by Habermann, who finds that a main essential for the successful working of the process is that the paper itself shall yield a coherent white ash. In the case of common varieties of paper, especially printing paper, which are loaded with china clay and other mineral matter, this condition is admirably fulfilled.