Of all these concomitants of errours, the letter of Dec. 10, in favour of elliptical arches, has afforded examples.  A great part of it is spent upon digressions.  The writer allows, that the first excellence of a bridge is undoubtedly strength:  but this concession affords him an opportunity of telling us, that strength, or provision against decay, has its limits; and of mentioning the monument and cupola, without any advance towards evidence or argument.

The first excellence of a bridge is now allowed to be strength; and it has been asserted, that a semi-ellipsis has less strength than a semicircle.  To this he first answers, that granting this position for a moment, the semi-ellipsis may yet have strength sufficient for the purposes of commerce.  This grant, which was made but for a moment, needed not to have been made at all; for, before he concludes his letter, he undertakes to prove, that the elliptical arch must, in all respects, be superiour in strength to the semicircle.  For this daring assertion he made way by the intermediate paragraphs, in which he observes, that the convexity of a semi-ellipsis may be increased at will to any degree that strength may require; which is, that an elliptical arch may be made less elliptical, to be made less weak; or that an arch, which, by its elliptical form, is superiour in strength to the semicircle, may become almost as strong as a semicircle, by being made almost semicircular.

That the longer diameter of an ellipsis may be shortened, till it shall differ little from a circle, is indisputably true; but why should the writer forget the semicircle differs as little from such an ellipsis?  It seems that the difference, whether small or great, is to the advantage of the semicircle; for he does not promise that the elliptical arch, with all the convexity that his imagination can confer, will stand without cramps of iron, and melted lead, and large stones, and a very thick arch; assistances which the semicircle does not require, and which can be yet less required by a semi-ellipsis, which is, in all respects, superiour in strength.

Of a man who loves opposition so well, as to be thus at variance with himself, little doubt can be made of his contrariety to others; nor do I think myself entitled to complain of disregard from one, with whom the performances of antiquity have so little weight; yet, in defiance of all this contemptuous superiority, I must again venture to declare, that a straight line will bear no weight; being convinced, that not even the science of Vasari can make that form strong which the laws of nature have condemned to weakness.  By the position, that a straight line will bear nothing, is meant, that it receives no strength from straightness; for that many bodies, laid in straight lines, will support weight by the cohesion of their parts, every one has found, who has seen dishes on a shelf, or a thief upon the gallows.  It is not denied, that stones may be so crushed together by enormous pressure on each side, that a heavy mass may safely be laid upon them; but the strength must be derived merely from the lateral resistance; and the line, so loaded, will be itself part of the load.