416 On the d[§-trent Theories of Arches, Vaults, &g: 



chain is of the arch, thai no correct conclusion can be ob-»' 

 tained: besides, the data are the reverse ut what are generally 

 given. 



In 1785, Mascheroni printed at Bergamo a work entitled 

 "Niioi't Rcchtrche suW EqnJlibrio tielit f'olie," which relate 

 principally to the equilibration of domes. 



In J 802, in consccjuence of a project submitted to the 

 House of Commons for building an iron arch over the 

 Thames, of 600 feet span, many eujinent tnathenialicians 

 were consulted ; and in their answers they were led to 

 the investigation of the subject of arches. 1 here were seven- 

 teen persons consulted ; their answers are in the third Re- 

 port Of the House of Connnons on the Improvenient of 

 the Port of London. IVlr. Alwood was induced to consider 

 the subject, and published -two tracts on it. His results are 

 the same as those of De la []ire, Parent, and Couplet. 

 Among the papers in the Rcjjort aliuderl to there is one by 

 Professor Roljistni, in which there is this element of 

 tijuilibration, " The load on every part of a circular arch 

 should be as the cube of a line drawn from the centre of 

 thcarch through that point, till it meet a horizontal line. 

 Thus the weights on ach (liii. (i) should be as od', qf^, Oe^j 

 <9 being the centre, and ds liorizontai. 



. In tlie i'hilosoi)hieal Magazine, vol. xi. Mr. Southern, of 

 Birmingham, published a paper on the equilibration of 

 arches, with a view to make Emerson's and Dr.Hutton'a 

 iheorv more easily understood. He was also one of the se- 

 venleen persons alluded to. 



ill 18ut2, Bossut, having reconsidered his papers published 

 in 1774 and 177G, republished them with additions, incor- 

 porating iheni into one memoir, at the end of his Traite de 

 JVJCcaiiKjUif. tie has treated ieparaiely of the equilibra- 

 tion of arches and domes. 



Dr. Oiinlluis Grtgorv, in his Treatise of Mechanics, ha9 

 extracted the most inicresiiiig propositions ol the Emerson 

 Ihetnv iiom the works of Emerson, Hutton,and the article 

 Arcli, in liie Supplement lo the Ency. Brit, by Professor 

 liobison. 



InDi.R^es's New Cyclopaedia the subject is invchtigatcd 

 under tiie articles Arch and JJiiJge, in which the Emerson 

 lueory has been adopted, and the propositions- &c. from 

 Emerson, [lutlou, and Robisjn have been inserted. There 

 IS also souie account given of the De 1a Hire tlieory, in 

 which, v\iih deference to the writer, ii apj;ears that that 

 tlieory has been wholly misunderstood, as well as the prac- 

 tice of arch building : for in the one case it is not necessary 



that' 



