THE windows offer a large and attractive field for decoration, so attractive and so useful that nothing but ignorance of the capacities of glass can be our excuse for overlooking it. It seems singular that at a time when art was still in the cradle, that branch of its development which culminates in painted glass should have been most encouraged, most advanced, and most popular. Giotto had scarcely breathed; Cimabue was discovering the laws of painting which gave permanent life to wood and stone; but many artists only a little inferior were combining colours in glass which we still admire and copy.

The reason of this is I think clear. When a wall is heavily decorated, as the walls in 'houses of worship' were from very early times, the blank left by a window - and windows must be admitted - is at once felt, like a shock to the eye. The more rich and intricate the colouring of the wall, the more the blank is felt, and the early windows which were only protected by a curtain or a shutter, before glass was invented, were probably an eye-sore to the eager decorators as well as a punishment to the shivering inhabitants. As soon as they devised a shield which did not exclude light they began to decorate it. The Romans used a transparent stone, lapis spccularis (mica?) and horn in the second century. The Moors and Persians used delicate wood-tracery in their windows even without glass, because the eye demanded it as much as to create shade - in fact a transparent shutter. The Chinese devised a thin stuff glazed with varnish or lac, polished oyster shells, and horn. In Gothic architectuie, when the walls are incrusted with carving, a sudden break in the ornament, which would be caused by a plain cut window, would be, I think, distressing, as is a hard, unsoftened edge in a picture; the shock is lessened by the internal arches being splayed off, and decorated with shafts and arch-mouldings running into elaborate patterns, these enclosing glass.

Thus the windows in Gothic architecture are carefully planned, both in form and in colour, to vary the scheme of ornament on the wall without too sudden a jar. They were actually transparent walls.

If they so calculated their framework, it is immediately clear how their eye would have resented a vast window of plate-glass, rectangular, colourless, like a breach in the wall. It is natural that coloured glass should have been employed both to carry out the adjacent colours and to utilise new spaces for the restless imagination, more especially as coloured glass existed before transparent white. I have before alluded to the importance of decoration when books were scarce and knowledge scarcer. A window which could admit light by which to better view the richness within, and meantime offer its own bright story or sermon - what a thrice welcome invention! How we can comprehend the labour and cost spent on so valuable an addition! As architecture advanced, the brilliancy and size of the windows advanced with it, till we arrive at such masterpieces of knowledge, fancy, and technical skill as the Rheims Cathedral.

Of course the use of coloured glass in mosaic is very old. The walls of Theodoric's palace at Rome were brilliant with pictures whose shining fragments still strew the waste ground, and from such use of glass the step to transparent mosaics in casements is not great. The first authors who speak of glass windows are St. Jerome and Gregory of Tours, who lived towards the end of the fourth century. St. Wilfrid, Archbishop of York, filled the vacant windows of the cathedral with glass about 669; in 674 Abbot Benedict Biscop brought artists from France to glaze those of the Abbey of Weremouth; and in 979 there were Venetian workmen, settled at Limoges, who drew from Byzantine traditions their skill in colouring glass. Glass mosaics may even have served as models for early glass paintings. About the end of the twelfth century coloured windows came into common use in churches, with the introduction of the pointed arch, and abolished the old tapestry curtain. These windows represented geometric patterns, or pictures, as desired: in the latter the figures were made of small pieces of self-coloured glass skilfully joined by leaden seams, but the faces were painted in enamel colours, and burnt in.

The first thing that strikes the eye in the windows of the best period of coloured glass (1200-1500) is, that the pieces of glass are so arranged and distributed as to form a kind of general brilliant mosaic of broken colour, which delights the eye from afar as a sunset does, the colours harmonising and playing into the perfect whole. This mosaic-look at once suggests the origin, wall-mosaics: it is so pronounced as to be almost confusing in very old windows; but as the art advanced there was no change in the scheme, though better drawing and better colours were introduced; the entire field was well and equally covered, and at a little distance no pattern was discernible to mislead or at once content the eye. On a nearer approach the patches of broken colour separate into subjects of increasing interest and charm, each little picture framed in stone-tracery distinct and well-contrasted, yet all the subjects being about equal in value of colour. The Bible heroes and angels are clearly defined, treated with a simplicity often amusing.

If you climb up close to the window, or reach it by walking along the clerestory - as how many a poor man, or unlettered noble, must have done listening to the good priest's exposition of the looming meanings! - more and more details appear: minute figures start into being; every bit of colour falls into robe or crown or wing, and is doubly accounted for; delicate borderings, naive details over and above the mere visibility of the subject startle us into fresh admiration and surprise. A strong opera-glass shows this without the trouble of ascent. Yet on dropping the glass, and moving far away again, the soft, shapeless, but beautiful mosaic melts into sunrise or sunset) or dusky colour once more - an indistinguishable whole. Thus the old windows offer three points of view in which to be thrice admired.

Some people fancy that this is owing only to the defective knowledge and skill of the old artists; but it seems probable that on the contrary the glass-paintefs knew and felt the double interest attaching to colour per se and colour as the vehicle of thought, and succeeded in giving both in their treatment of window-decoration. The difficulty of fusing large sheets of glass in old times may have partly accounted for the absence of large masses of plain colour; still they must have known (as we know directly we try the experiment) that small pieces of glass can be arranged in a far more interesting and surprising manner than large sheets. Even latticed windows are more beautiful than big panes, because the pattern of the leading carries decoration into a place where we moderns admit none. The coloured cathedral windows are often masterpieces of art-ingenuity which, without greatly excluding light, invest the whole gorgeous fabric of Gothic architecture with a 'dim religious' charm, no doubt indispensable to harmony when the cathedrals were new, and internally coloured throughout as richly as the Alhambra itself; but even now, in their semi-whitewashed condition of renovated old age, the old windows remain the one link of living colour that revives the keynote of the whole.