a 2 6 MlfceUanea Curio fa . 



the only Genuine Arches or Fornixes. And 

 an Arch of any other Figure, is for this 

 reafon only, fuftain'd, becaufe a Catenaria is 

 included in the thicknefs of it. For if it 

 were very thin, and confifted of parts that 

 were flippery, it would not be fuftain'd. 

 From the foregoing fifth Corol. it may be ga- 

 ther'd with what force an Arch thrufts the 

 Walls outwards, that it ftands upon for 

 this is the very fame with that part of the 

 force (fuftaining the Catena) which draws 

 with the Horizontal dire&ion. All other 

 Matters requir'd in the ftrength and firm-" 

 nefs of Walls, that have Arches fet upon 

 them, are Geometrically deter mi n'd from 

 this Theory; which are the principal Things^ 

 in Building. 



COROL. VII. 



If inftead of Gravity, any other force were 

 fuppos'd acting in like manner upon a flexi- 

 ble Line, the fame Curve would be produced. 

 Ex.gr. Suppofe a Wind blowing equably, 

 and in directions parallel to a given right 

 Line, the Line thus inflated by the Wind, 

 would be the fame with the Catenaria. For 

 iince all things that were confider'd in Gra- 

 vity, obtain iri this other force, 'tis plain 

 that the fame Curve will be produced. 



PROP. 



