144 THE STONES OF VENICE CONSTRUCTION

overhang its base a foot or two, as you may see any day in the gravelly banks of the lanes of Hampstead: but make the bank of gravel, equally loose, six hundred feet high, and see if you can get it to overhang a hundred or two! much more if there be weight above it increased in the same proportion. Hence, let any capital be given, whose projection is just safe, and no more, on its existing scale; increase its proportions every way equally, though ever so little, and it is unsafe; diminish them equally, and it becomes safe in the exact degree of the diminution.

Let, then, the quantity e d, and angle d b c, at A of Fig. 23, be invariable, and let the length d b vary: then we shall have such a series of forms as may be represented by

a, b, c, Fig. 24, of which a is a proportion for a colossal building, b for a moderately sized building, while c could only be admitted on a very small scale indeed.

§ 16. (3.) The greater the excess of abacus, the steeper must be the slope of the bell, the shaft diameter being constant.

This will evidently follow from the considerations in the last paragraph; supposing only that, instead of the scale of shaft and capital varying together, the scale of the capital varies alone. For it will then still be true, that, if the projection of the capital be just safe on a given scale, as its excess over the shaft diameter increases, the projection will be unsafe, if the slope of the bell remain constant. But it may be rendered safe by making this slope steeper, and so increasing its supporting power.

Thus let the capital a, Fig. 25, be just safe. Then the

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