« ElőzőTovább »
Dec. 15, 1759. It is the common fate of erroneous positions, that they are betrayed by defence, and obscured by explanation ; that their authors deviate from the main question into incidental disquisitions, and raise a mist where they should let in light.
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 con. cession 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 semiellipsis has less strength than a semicircle. To this he first answers, that granting this position for a inoment, the semi-ellipsis may yet have strength sufficient for the purposes of commerce. 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 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, laidin straightlines,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.
The semi-elliptical arch has one recommendation yet unexamined; we are told that it is difficult of execution. Why difficulty should be chosen for its own sake, I am not able to discover ; but it must not be forgotten, that as the convexity is increased, the difficulty is lessened ; and I know not well whether this writer, who appears equally ambitious of difficulty and studious of strength, will wish to increase the convexity for the gain of strength, or to lessen it for the love of difficulty.
The friend of Mr. M, however he may be mistaken in some of his opinions, does not want the appearance of reason, when he prefers facts to theories; and that I may not dismiss the question without some appeal to facts, I will borrow an example, suggested by a great artist, and recommended to those who may still doubt which of the two arches is the stronger, to press an egg first on the ends, and then upon the sides.
I am, SIR,
Both ANCIENT and MODERN:
With an Account of the Honour due to an
ENGLISH FARMER *.
AGRICULTURE, in the primeval ages, was
the common parent of traffick : for the opulence of mankind then consisted in cattle, and the product of tillage; which are now very essential for the promotion of trade in general, but more particularly so to such nations as are most abundant in cattle, corn, and fruits. The labour of the Farmer gives employment to the manufacturer, and yields a support for the other parts of the community: it is now the spring which sets the whole grand machine of commerce in motion ; and the sail could not be spread without the assistance of the plough. But though the Farmers are of such utility in a state, we find them in general too much
* From the Universal Visitor, for February 1756, p. 59.Smart, the poet, had a considerable hand in this Miscellany. The very first sentence, however, may convince any reader that Dr. Johnson did not write these “ Thoughts"; they are inserted here merely as an introduction to “The Further Thoughts," which follow, and which are undoubtedly his.
disregarded among the politer kind of people in the present age; while we cannot help observing the honour that antiquity has always paid to the profession of the husbandman; which naturally leads us into some reflections upon that occasion. .
Though mines of gold and silver should be exhausted, and the species made of them lost; though diamonds and pearls should remain concealed in the bowels of the earth, and the womb of the sea; though commerce with strangers be prohibited; though all arts which have no other object than splendour and embellishment, should be abolished; yet the fertility of the earth alone would afford an abundant supply for the occasions of an industrious people, by furnishing subsistence for them, and such armies as should be mustered in their defence. We, therefore, ought not to be surprized, that Agriculture was in so much honour among the ancients : for it ought rather to seem wonderful that it should ever cease to be so, and that the most necessary and most indispensable of all professions should have fallen into any contempt.
Agriculture was in no part of the world in higher .consideration than Egypt, where it was the particular object of government and policy: nor was any country ever better peopled, richer, or more powerful. The Satrapæ, among the Assyrians and Persians, were rewarded, if the lands in their governments were well cultivated; but were punished if that part of their duty was neglected. Africa abounded in corn; but the most famous countries were Thrace, Sardinia, and Sicily.
Cato, the censor, has justly called Sicily the ma