Analysis of information sources in references of the Wikipedia article "Skew arch" in English language version.
Arches of great obliquity are much the strongest when constructed with a segmental elevation; whether the segment of a circle or an ellipse, is of little importance, so long as the rise is between a third and sixth of the span of the semi-figure. The more oblique the plan of the bridge, the greater is the necessity for keeping the arch flat; and for the following reasons. All semi-arches built with spiral courses are strongest at the summit, because the stones in that position approach nearer to a right angle than in any other; therefore, the more remote from the summit, the more weak the arch will unavoidably be; consequently, as they near the horizon, they decrease in strength and beauty, as they increase in cost and difficulty of construction.
When the bed joints are of such a form that the arch is in equilibrium without friction, the courses are called the equilibrated courses
When a road crosses a canal in an oblique direction, the bridge is often made oblique. When the angle does not vary more than ten or twelve degrees from a right angle, the arch-stones may be formed as already described; but in cases of greater obliquity, a different principle of construction is necessary. These cases should, however, be avoided wherever it is possible; as, however solid the construction of an oblique bridge may be in reality, it has neither the apparent solidity nor fitness which ought to characterize a useful and pleasing object.
The stones were cut, or dressed, previously to the erection of the centre
No one would for a moment hesitate to acknowledge the obligations which practical men are under to that highly talented individual Mr Peter Nicholson; but on referring to his Treatise on Masonry and Stone-cutting (plate 17) it will at once appear that the intrado is the only surface developed, and the approximate line laid down upon it, all the courses are drawn at right angles to that line; the courses therefore are drawn with reference to the intrado only
It is really very lamentable to see a man of the standing Peter Nicholson once had, obliged to have recourse to so mean and unworthy subterfuge; and it is still more lamentable to see him forget himself so much in the language he makes use of. [...] Is he ignorant of the fact that Mr. Buck has surmounted this difficulty by the simple expedient of adjusting the angle of the intrado—or is it that, rather than acknowledge his inferiority, he persists in what he knows to be wrong, and addresses his book to the working classes in the hope of escaping detection? [...] It is perfectly distressing to see a problem which admits of easy solution so miserably mutilated in his hands. [...] Mr. Nicholson's rules however are not only very unnecessarily tedious, but it would appear by his own showing, that they are not over certain in their results. [...] However, I will say no more. For this time I have, as he observes, "done with him" and I hope enough has been said to show Mr. Nicholson that his ideas have got a twist in their beds by no means adapted to skew-bridges, and that no species of brow-beating or invective on his part will be of the slightest use to him, while his book remains so very imperfect
On [Truesdell's] death in 1909, the Association of Engineering Societies' Journal characterized the Seven [sic] Street Improvement Arches as 'the most important piece of masonry in the city'.
