14.

confirmed by practice, and by the buildings of thetimes when arches were most in use and not con-demned by them. When truth appears, she is mani-fest to the ordinary gaze; but at present the mosteminent engineers seem to have obtained a veryimperfect sight of her. For example: by referenceto the tables of bridges, assuming the radius ofcurvature at the vertex a measure of the strength ofa bridge in respect to figure; and the strength andweight of the material, and the incumbent weight,constant ; it appears that Perronet, with ordinarystone, though so timid as to think it prudent to makethe bridge of Neuilly * twelve times stronger thana breaking strength, performed more than is per-formed at the bridge of Conan t, in Ross-shire, in

* It will be said that there are some settlements in the bridgeof Neuilly ; but they have little relation to the matter in question.

f The Report of the Commissioners for Roads and Bridges inthe Highlands of Scotland has just fallen into the author’s hands,in which there is an account of 1117 bridges, and drawings of 37.There is given the water-way of the bridges, but no relative water-way of the rivers; and, what is very extraordinary in the presentstate of knowledge, all the arches of which drawings are givenare arcs of circles. The spans of the arches are given, but onlyin two instances are the versed sines. In no instance is the height ofthe key-stone given, nor the widths and heights of the abutmentsand bearing piers, nor the steepness of the roads over the bridges,except by a very small scale, which cannot be relied upon for suchobjects of inquiry. In this report the commissioners are made tosay of their engineer, “ that in all his plans and estimates ofbridges and other masonry, he has manifested the most scru-pulous economy, as never having been induced, by too muchanxiety for his own character, to recommend needless solidity atthe expense of his employers, we were obviously induced tosecure his services," &c. This is a proper remark, if intended asa reproof to any one in particular, whose fears bias his judgmentbut the application cannot be meant generally, which the con-sequence would warrant. In such a report, some disappoint-ment must occur in not finding a demonstration of the fact. The