If for instance we take a cathedral, any one of a series—let us say of Paris; when completed, or nearly so, it was easy to see that though an improvement on those which preceded it, there were many things in its construction or design which might have been better. The side-aisles were too low, the gallery too large, the clerestory not sufficiently spacious for the display of the painted glass, and so on. Let us next suppose the Bishop of Amiens at that period determined on the erection of his cathedral. It was easy for him or his master-mason to make these criticisms, and also to perceive how these mistakes might be avoided; they could easily see where width might be spared, especially in the nave, and where a little additional height and a little additional length would improve the effect of the whole. During the progress of the Parisian works also some capitals had been designed, or some new form of piers adopted, which were improvements on preceding examples, and more confidence and skill would also have been derived from the experience gained in the construction of arches and vaults. All these of course would be adopted in the new cathedral; and without making drawings, guided only by general directions as to the plan and dimensions, the masons might proceed with the work, and, introducing all the new improvements as it progressed, they would inevitably produce a better result than any that preceded it, without any especial skill on the part either of the master-mason or his employer. If a third cathedral were to be built after this, it would of course contain all the improvements made during the progress of the second, and all the corrections which its results suggested; and thus, while the art was really progressive, it required neither great individual skill nor particular aptitude to build such edifices as we find. In fine arts we have no illustration of this in modern times; but all our useful arts advance on the same principles, and lead consequently to the same results. In ship-building, for instance, as mentioned in the Introduction (page 45), if we take a series of ships, from those in which Edward III. and his bold warriors crossed the channel to the great line-of-battle ships now lying at anchor in our harbours, we find a course of steady and uninterrupted improvement from first to last. Some new method is tried; if it is found to succeed, it is retained; if it fails, it is dropped. Thus the general tendency constantly leads to progress and improvement. And, to continue the comparison a little further, this progress in the art is not attributable to one or more eminent naval architects. Great and important discoveries have no doubt been made by individuals, but in these cases we may generally assume that, the state of science being ripe for such advances, had the discovery in question not been made by one man, it soon would have occurred to some other.