229.  So much, then, for position.  We have now only to settle the questions of form and color, and we shall then have closed the most tiresome investigation which we shall be called upon to enter into; inasmuch as the principles which we may arrive at in considering the architecture of defense,[51] though we hope they may be useful in the abstract, will demand no application to native landscape, in which, happily, no defense is now required; and those relating to sacred edifices will, we also hope, be susceptible of more interest than can possibly be excited by the most degraded branch of the whole art of architecture, one hardly worthy of being included under the name—­that, namely, with which we have lately been occupied, whose ostensible object is the mere provision of shelter and comfort for the despicable shell within whose darkness and corruption that purity of perception to which all high art is addressed is, during its immaturity, confined.

[Footnote 51:  [Referring again to the intended sequel.]]

230.  There are two modes in which any mental or material effect may be increased—­by contrast, or by assimilation.  Supposing that we have a certain number of features or existences under a given influence; then, by subjecting another feature to the same influence, we increase the universality, and therefore the effect, of that influence; but by introducing another feature, not under the same influence, we render the subjection of the other features more palpable, and therefore more effective.  For example, let the influence be one of shade, to which a certain number of objects are subjected.  We add another feature, subjected to the same influence, and we increase the general impression of shade; we add the same feature, not subjected to this influence, and we have deepened the effect of shade.

Now, the principles by which we are to be guided in the selection of one or other of these means are of great importance, and must be developed before we can conclude the investigation of villa architecture.

231.  The impression produced by a given effect or influence depends upon its degree and its duration.  Degree always means the proportionate energy exerted.  Duration is either into time, or into space, or into both.  The duration of color is in space alone, forming what is commonly called extent.  The duration of sound is in space and time; the space being in the size of the waves of air, which give depth to the tone.  The duration of mental emotion is in time alone.  Now in all influences, as is the degree, so is the impression; as is the duration, so is the effect of the impression; that is, its permanent operation upon the feelings, or the violence with which it takes possession of our own faculties and senses, as opposed to the abstract impression of its existence, without such operation on our own essence.

For example, the natural tendency of darkness or shade is to induce fear or melancholy.  Now, as the degree of the shade, so is the abstract impression of the existence of shade; but as the duration of shade, so is the fear or melancholy excited by it.