Descriptions and illustrations of nearly all the monuments mentioned will be found in Dr. J. Stuart’s _Sculptured Stones of Scotland_ (published by the Spalding Club of Aberdeen); Dr. J. Anderson and J. R. Allen’s _Early Christian Monuments of Scotland_ (published by the Society of Antiquaries of Scotland); R. C. Graham’s _Carved Stones of Islay_; H. O’Neill’s _Sculptured Crosses of Ancient Ireland_; Dr. Petrie’s _Christian Inscriptions in the Irish Language_ (published by the R. Soc. Ant. of Ireland); Miss M. Stokes’ _Early Christian Art in Ireland_; Prof. J. O. Westwood’s _Lapidarium Walliæ_; A. G. Langdon’s _Old Cornish Crosses_; J. G. Cumming’s _Runic Remains of the Isle of Man_. The Celtic metalwork of the Christian period may be arranged under the following heads:— Bells. Book-shrines. Croziers. Relic shrines. Chalices. Plaques for book-covers. Processional crosses. Penannular brooches. Bell-shrines. Hammer-headed pins. With a few exceptions all the existing specimens are now preserved in the Museum of the Royal Irish Academy in Dublin, the National Museum of Antiquities of Scotland in Edinburgh, and the British Museum in London. Ecclesiastical bells are of two different kinds, namely, (1) _portable_ bells, sufficiently light to be carried in the hand; and (2) _fixed_ bells, whose weight renders a trussed framework of wood necessary for their support. Each kind of bell can be rung in two separate ways, namely, (1) by holding the bell stationary and striking it on the outside with a hammer; or (2) by providing the bell with a tongue, or clapper, suspended from the inside and swinging the bell backwards and forwards, so as to cause the clapper to strike against the interior and thus produce sound. The method of bell-ringing by means of a hammer is frequently illustrated in the illuminated psalters of the thirteenth and fourteenth centuries, and is also to be seen on the sculptured capitals in the Abbey of St. George’s de Boscherville,[385] in Normandy. The great bells of the Kremlin at Moscow, and in other Greek churches throughout Russia, are rung in this fashion. Portable bells with clappers have a handle at the top, by which they can be swung backwards and forwards in the hand, in the manner depicted upon the Bayeux Tapestry.[386] Fixed bells with clappers have loops at the top for suspension by iron bands to a horizontal wooden axle or rocking bar working in bearings supported on a trussed framework of timber, usually within a masonry tower. The required rocking motion is given by a lever and rope or a grooved wheel and rope.