These three points of contrast will be quite enough: there is no other external influence from which we can free the building, and the pervading energy must be communicated to it, or it will not harmonize with our feelings; therefore, before proceeding, we had better determine how this contrast is to be carried out in detail. 243. Our lines are to be horizontal; then the roof must be as flat as possible. We need not think of snow, because, however much we may slope the roof, it will not slip off from the material, which, here, is the only proper one; and the roof of the cottage is always very flat, which it would not be if there were any inconvenience attending such a form. But, for the sake of the second contrast, we are to have gracefulness and ease, as well as horizontality. Then we must break the line of the roof into different elevations, yet not making the difference great, or we shall have visible verticals. And this must not be done at random. [Illustration: Fig. 14. Leading lines of Villa-composition.] 244. Take a flat line of beauty, _a d_, fig. 14, for the length of the edifice. Strike _a b_ horizontally from _a_, _c d_ from _d_; let fall the verticals, make _c f_ equal _m n_, the maximum; and draw _h f_. The curve should be so far continued as that _h f_ shall be to _c d_ as _c d_ to _a b_. Then we are sure of a beautifully proportioned form. Much variety may be introduced by using different curves; joining parabolas with cycloids, etc.; but the use of curves is always the best mode of obtaining good forms.[55] [Footnote 55: [Compare _Modern Painters_, vol. IV. chap. xvii. Sec. 49, and _Elements of Drawing_, Letter III.]] Further ease may be obtained by added combinations. For instance, strike another curve (_a q b_) through the flat line _a b_; bisect the maximum _v p_, draw the horizontal _r s_, (observing to make the largest maximum of this curve towards the smallest maximum of the great curve, to restore the balance), join _r q_, _s b_, and we have another modification of the same beautiful form. This may be done in either side of the building, but not in both. 245. Then, if the flat roof be still found monotonous, it may be interrupted by garret windows, which must not be gabled, but turned with the curve _a b_, whatever that may be. This will give instant humility to the building, and take away any vestiges of Italian character which might hang about it, and which would be wholly out of place.