15
different ages are amusing. In the groined vault wemay perceive the origin of all the improvements whichthe Free Masons made in the art of vaulting.
The Romans, in their bridges, -endeavoured to re-duce the size of the piers of their bridges, and to ren-der the vaults of their arches more nearly in equili-bration, than the line of road would generally permit,by means which, in some measure, surprise us by theirclumsiness, when the more elegant mode by groinedvaulting had been discovered. The practice to reducethe size of the piers was by constructing small archesin the piers themselves, above that part of the pierwhere adequate resistance had been obtained for thelateral thrust of the arch ; as may be seen in the Pontdu Saint Esprit over the Rhone , in Languedoc , at thebridge of Merida, in Spain , and Ponte Fabrizio, atRome . A similar mode was adopted at the Ponte Senatorio now Ponte Rotto , by Pope Gregory XIII . This method had also the additional ad-vantage of affording more water-way. Tunnels havebeen sometimes worked in the piers with the sameview, as in Ponte Sisto , built by Pope Sextus IV. uponthe site of the ancient bridge of Janiculense, and as atthe Pont de Toulouse, in France , and at the bridge ofGlasgow , over the Clyde. Perronet, the French archi-tect, not only formed tunnels in the piers, but alsoover the haunches. The Welch mason Edwards, inthe wonderful bridge over the Taafe, in Glamorgan shire , learnt, from experience, what Perronet’s theoryhad taught him. Over each haunch of the arch ofthe Pont-y-ty-Prydd, there are three tunnels in thereins of the arch. The mode recommended to beadopted at Blackfriars’ Bridge, by Dr. Stukely, Phil.