in equal times, which plays so important a part in musical form, is discernible in architecture as a rhythm in space.  We may treat a cottage type of design, no doubt, with a playful irregularity, especially if this follows and is suggested by an irregularity, of plan.  But in architecture on a grand scale, whether it be in a Greek colonnade or a Gothic arcade, we cannot tolerate irregularity of spacing except where some constructive necessity affords an obvious and higher reason for it.  Then, again, we find the unwritten law running throughout all architecture that a progress of line in one direction requires to be stopped in a marked and distinct manner when it has run its course, and we find a similarly felt necessity in regard to musical form.  The repetition so common at the close of a piece of music of the same chord several times in succession is exactly analogous to the repetition of cross lines at the necking of a Doric column to stop the vertical lines of the fluting, or to the strongly marked horizontal lines of a cornice which form the termination of the height or upward progress of an architectural design.  The analogy is here very close.  A less close analogy may also be felt between an architectural and a musical composition regarded as a whole.  A fugue of Bach’s is really a built-up structure of tones (as Browning has so finely put it in his poem, “Abt Vogler"), in accordance with certain ideas of relation and proportion, just as a temple or a cathedral is a built-up structure of lines and spaces in accordance with ideas of relation and proportion.  Both appeal to the same sense of proportion and construction in the brain; the one through the ear, the other through the eye.  Then, in regard to architecture again, we have further limiting conditions arising not only out of the principle of construction employed, but out of the physical properties of the very material we employ.  A treatment that is suitable and expressive for a stone construction is quite unsuitable for a timber construction.  Details which are effective and permanent in marble are ineffective and perishable in stone, and so; on and the outcome of all this is that all architectural design has to be judged, not by any easy and ready reference to exterior physical nature, with which it has nothing to do, but by a process of logical reasoning as to the relation of the design to the practical conditions, first, which are its basis, and as to the relation of the parts to each other.  Of course beyond all this there is in architecture, as in music, something which defies analysis, which appeals to our sense of delight we know not how or why, and probably we do not want to know; the charm might be dissolved if we did.  But up to this point architectural design and expression are based on reasoning from certain premises.  The design is good or bad as it recognizes or ignores the logic of the case, and the criticism of it must rest on a similar basis.  It is a matter of thought in both cases, and without thought it can neither be designed nor appreciated to any purpose, and this is the leading idea which I wish to urge and to illustrate in these lectures.