A learned dissertation on clocks and the theory of time would be out of place in a volume of this description, and anything we have to say concerning the clocks of the "walnut period" will, of necessity, be of a popular nature. In England the chamber clocks, as distinguished from the costly and elaborate timepieces which adorned public buildings, appear to have been introduced about the year 1600.[6] The type is fairly familiar, and is known as the "lantern," "bird-cage," or "bedpost." Amongst dealers such clocks are usually styled "lantern" or "Cromwell." They usually stood on a wall-bracket, but sometimes were suspended from a nail. The clocks are built of brass surmounted by a bell, sometimes used for striking the hours and sometimes only for an alarm. The clocks were often housed in hooded oak cases, which protected them from the dust. [6] Strictly speaking, De Vyck's clock, invented about 1370, is the earliest known type of the domestic clock. Made for the wealthy few in days when the generality of people did not look upon clocks as necessities, they only exist to-day as rare museum specimens. These original cases are sometimes met with and are interesting in themselves, but the brass clocks are more ornamental when minus the cases. These clocks were made to run for thirty hours, the motive power being a heavy weight with a cord or chain. At first the vertical verge movement was used, but about 1658 the pendulum was introduced. The alternate bobbing in and out of the short pendulum through slits in either side of the clock accounts for the term "bob" pendulum. It has been noticed that the doors of these early clocks were often constructed from old sundial plates, the engraved figures of the sundial still showing on the insides. Doubtless the sundial makers, finding their trade falling off, used the materials in hand for the new-fangled clocks. The dial-plate of the early lantern clock is circular, with a band of metal (sometimes silvered) for the numerals, which at first were rather short. About 1640 the hour-hands were made wider and the numerals longer. After about 1660, we find the circular dial growing larger in relation to the body of the clock and protruding slightly on either side. During the latter years of Queen Anne's reign the dial-plates often protruded as much as two or three inches on either side. This did not improve the general appearance. Clocks of this pattern are known as the "sheep's head." With such slight variations the lantern clock was made from Elizabeth's to George III.'s reigns. The late ones, probably made by provincial clock-makers, have square dials with arched tops.