A friend and correspondent, whose opinion is entitled to attention,
questions the novelty of Mr. Hosx.rNo's "longitudinal central groin- ing through the arches of a bridge : "it has been largely used," he observes, "in the construction of arches by Mr. Brunel junior." He instances the Wharncliffe viaduct at Hanwell, as a case in point ; and directs our attention to "the perspective through the arches of that viaduct." We had seen and admired this striking effect; and we had also admired the extreme lightness and elegance of the whole structure: the wide span and graceful curve of the cycloidal arches render them very beautiful. But we fear that our description of Mr. flea- KING'S longitudinal groining must have been defective, to lead our correspondent to the conclusion that it is exhibited in the Wlsarn- cliffe viaduct. The piers of this land-bridge are divided into two square brick pillars, coupled on one base ; but the arches they support are solid—if we recollect rightly, they are neither groined nor per- forated. Now, the groining of Mr. HOMING perforates the arches, not the piers; its object being, as we understand his book, to lighten the superstructure, and enable the bridge-builder to dispense with the in- ternal spandril or haunch walls, by carrying the thrust of the whole series of arches through to the abutments of each end, and checking the vibration caused by heavy traffic. Indeed, thc piers of the bridge, according to Mr. HOMING'S plan, are not perforated at all : the spring- ing of the arches of his longitudinal groining is above the level of high- water, being from the same line as the springing of the arches of the water-way. In short, Mr. BRUNEL'S improvement, lightening the supports of land-bridges of lofty elevation, is totally distinct from Mr HOMING'S proposition for lightening the superincumbent weight of low bridges over rivers.
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