Scotch wooden lock in the Patent Museum at South Kensington, a facsimile of which is in my collection. Figs. 18A to 22A, Plate II., is another, also in the Patent Museum, in which three tumblers instead of two are raised by the same key, as shown in the sections, figs. 21A and 22A, Plate II. Mr. ROMILLY ALLEN, who has written a paper on Scotch tumbler locks in the 2nd volume, New Series, of the 'Proceedings of the Society of Antiquaries of Scotland,' figures several others of the same class. One from North Ronaldsay has four tumblers in line; another from the Faroe Islands has three tumblers in line; another from Snizort, in Skye, has six tumblers working independently of each other but raised with the same key, and consists simply of two ordinary locks put face to face with the bolt between them; another from Harris is still more complicated in its construction, and is formed by five tumblers in line with two holes running through the whole of them, and the key has two limbs, one for each line of holes. It is unnecessary for my present purpose to describe all these locks in detail. Though varying in character they are all constructed on one principle. As with the more complicated contrivances in metal, hereafter noticed, variety is an element of security, the greater the variety, the greater the difficulty of making a key which will fit them all; and this is another point in which the processes of the arts resemble the processes of nature, variety adapts the mechanism to a wider sphere of utility, and by encouraging change, promotes improvement. In the one, as in the other, variation is a necessary element of progress.