10

OF CYLINDRICAL VAULTS.

Angelo is justly condemned for neither imitating thevaults of the Temple of Peace * (Pig. 5.), nor the

space 1031 feet in length, and of any width (the angle at the pointsof suspension being only 7° 10 f .); hence an iron roof only aninch thick might be safely suspended over a quadrangle whoseshortest side would be 251 feet longer than the longest side ofLincoln’s Inn Fields, without any support except from the sidewalls. By the theory that “ what appertains when suspended andflexible, appertains when inverted and rigidan arched roof mightbe erected over the same space, in the same form, of the samematerial and of the same thickness, supposing the cohesion ofiron to be the same, in the state of compression, as of tension. Wehave not yet data to enable us to determine the maximum ordinateto a given angle at the springing, or the minimum angle to a givenordinate, of a stone arch, nor the thickness of a stone arch to a givenangle and ordinate. Messrs. Walkers, of Rotherham , lately con-structed for the Birmingham theatre a very flat dome, about sixtyfeet on the chord line, of plate iron about half an inch thick with-out any ribs, intended to serve both for a ceiling and a roof; but, inconsequence of an accident which happened to a cast-iron beam, aprejudice was taken against iron, and the dome has not beenfixed.

Pliny , lib. xix. cap. 1., says, “ Carbasina deinde vela primusin theatro duxisse traditur Lentulus Spinter Appollinaribus ludis.”Carlo Fontana , in his L’Anfiteatro Flavio, shews how a space whichwould contain 100,000 persons, that is, an ellipse whose axes are550 by 450 feet, was covered by the Romans from the walls withoutany support from below. Maffei (cap. 14. De gli Anfiteatri) has achapter on the velario used in covering amphitheatres; perhaps theintroduction of pendent iron bridges may introduce iron velarios.The velarian curve, John Bernouilli (vol. iii. p. 112.) shews to be thesame as the catenaria. If Cheops , the builder of the great pyramid,had left a bulk of masonry 777 feet square at its base, and 478 high,enclosing a hollow space; Grobert (see Descr. des Pyram.) would nothave exclaimed, “ Comme l’ami de la veritc est irrite des exclama-tions de ces voyageurs romanesques, qui associent l’idee du beau a.celle de l’£normit6 : qui ont voulu deviner les efforts de l’art la ohl’on n’aper^mit que la patience et la fatigue d’une nation asservie.”

* The vault of the Temple of Peace at Rome is 83 feet wideand 121 feet high.