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The careful analyst will occasionally wish to identify the first formes in a book under investigation; often, perhaps, to check someone else's assumption that the inner forme was regularly printed first, or to verify a plausible interpretation of skeletons or press-figures. In a crisp, unpressed copy it is usually possible to recognise the first forme by the indentations of the second — a little hillock with ink on its surface occurs wherever a letter in the first-forme page has been indented by a letter of the second forme. This is the easiest way to tell whether an incunable was printed page by page; if, for example, the four pages of a folio sheet were printed in page order, both rectos will bear first-forme impressions and both versos second-forme. In the detection of cancels and similar problems of conjugacy, the method is an alternative to the use of evidence from the indentations of the mould on laid paper and a substitute for it if wove paper is in question.[1] It is the best means of distinguishing concurrent from consecutive perfecting, a matter of great importance in the study of variant formes. If the two formes of a sheet were laid on by two presses at the same time and the pressmen exchanged heaps half-way through the impression, each perfecting the other's work, half the sheets will have first-forme impressions of the outer forme and half of the inner.[2] And as I have pointed out elsewhere, the relationship between indentations will serve to distinguish common imposition in half sheets from the imposition called 'two half sheets worked together'.[3]
It is usually very difficult to find a copy in which the unaided eye can recognize the first forme, and the difficulty is more than doubled in some cases by the necessity of comparing two such copies. I have to thank a colleague, Mr. D. G. E. Martin, for advice on the use of optical apparatus to increase the amount of evidence that can be extracted from reluctant-looking material. The requirement is a parallel beam of light which can be directed onto a page of the book, lying within the beam and parallel to it.
But microscope lamps are expensive and not easily portable and they depend on the availability of a suitable source of current. It is simple to make a collimator without these disadvantages and effective enough if it is used in a nearly dark room. Bibliographers may, if they wish, call it the Martin Lamp. The device consists of (1) an ordinary front bicycle lamp with a head about 2⅜" in diameter; its normal battery and bulb are used but the glass must be removed and the reflector blackened; (2) a tube, which can be made of rolled paper, to fit on the head of the lamp; (3) a convex lens of similar diameter fixed in the front end of the tube with adhesive tape. A cheap reading-glass with a focal length of about 7" will do very well. The distance between the lens and the source of light (A-B in the diagram) must be equal to the focal length of the lens, and that can be found by measuring the distance from a sheet of paper at which the lens gives the sharpest image of a distant object, for example, some detail of a building across the street. A piece of lead should be put in the slot at the back of the lamp to balance the weight of the tube and lens. No more apparatus is needed because the book can if necessary be supported on another of convenient size and the lamp can be held in the best position by hand.[*]
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