X

At the time the author was engaged in the in -vestigation of the principles of pendent bridges,Mr. Davies Gilbert ’s Letter to the Editor of theJournal of Science, Roy. Inst. No. 20. “ On someProperties of the Catenarian Curve, with re-ference to Bridges by Suspension*,” fell into hishands, in which a property is elicited, that acatenary of certain dimensions admits of a mini-mum tension corresponding to a given ordinate,or a maximum ordinate to a given tension ; hewas hence induced to consider this property ofthe catenary which he believes was not known,or at least not noticed before the publication ofMr. Gilbert ’s letter, and he availed himself ofthe assistance of Mi*. G riffith Davies, of CannonStreet, by whose aid a new and simple methodof constructing that curve has been obtained;and, as a corollary to it, a mode by which a loga-rithmic curve may be drawn to a given sub-tangent.

The table of the dimensions of the catenarywas at first calculated by assuming the tension

*' In No. 10 . Oct. 1821 , Edin, Phil. Journ., there is a de-scription of some bridges of suspension, by Robt. Steven-son, Esq. and in No. 11. Jan. 1822 , of a pier of suspensionat Newhaven, near Edinburgh , by Cap. S. Brown. InDouglas’ Mil. Brid. a rope bridge used at Alcantara is de-scribed. Tract 3 . was printed many months before theauthor saw these works, or he would have availed himself ofthe illustration which the demolition of the pendent bridge atDrybnrgb affords of the principles he has deduced in respectto such bridges. See Tract 3 . pages 28 . 43 .