An investigation of the books of the period reveals the fact that the same blocks were used by different printers. Articles have been written on the migration of printer's blocks, but, so far, no explanation has been offered as to any object other than decoration for which these blocks were used. Among other designs in use between 1576 and 1640 are a number of variants of a device in which a light A and a dark A form the most conspicuous points. Camden, in his "Remaines Concerning Britaine," 1614, commences a chapter on "Impresses," at the head of which the device is found, thus:--"An Imprese (as the Italians call it) is a device in picture with his Motto, or Word, borne by noble and learned personages, to notifie some particular conceit of their owne: as Emblemes (that we may omitte other differences) doe propound some general instructions to all." Then follow a number of examples, and amongst them this:-- "Variete and vicissitude of humane things he seemed to shew which parted his shield, Per Pale, Argent & Sables and counter-changeably writte in the Argent, Ater and in the Sables Albus." But even if the light A and dark A are used in the design of the head-piece to represent Albus and Ater it does not afford any satisfactory explanation as to why they are so used. In MDCXVI. was published "Les Emblemes Moraulx et Militaires du Sieur Jacob De Bruck Angermundt Nouvellement mis en Lumiere A Strasbourg, Par Jacob de Heyden Graveur." In Emblem No. 18, now reproduced, the light A and the dark A will be found in the branch of the tree which the man is about to cut off. (Figure VI.)[44] Another Emblem does not contain the light A and dark A, but the bark of the trunk and branches of the tree on the design exhibit a strong contrast between the dark and light, which feature is represented in most of the title-pages of books in which the device is found. (Figure VII.) Mr. Charles T. Jacob, Chiswick Press, London, who is the author of "Books and Printing" (London, 1902), and several works on typography, referring to an article on the migration of woodblocks, said:--