ABSTRACTS OF SCIENTIFIC PAPERS 363 



quoted put at their disposal a remarkably simple and accurate 

 method of calculating the stresses in framework ; and the author's 

 attention was drawn to the method chiefly by the circumstance that 

 it was independently discovered by a practical draughtsman, Mr. 

 Taylor, working in the office of the well-known contractor, Mr. J. B. 

 Cochrane. The object of the present paper is to explain how the 

 principles above enunciated are to be applied to the calculation of 

 the stresses in roofs and bridges of the usual forms.' 



The construction of reciprocal figures for various typical forms of 

 bridge and roof trusses, under vertical and horizontal loads, is then 

 explained fully and illustrated by a large number of diagrams. 

 [In this connection reference may also be made to 52-56 of Pro- 

 fessor Jenkin's article on BRIDGES in the ' Encyclopaedia Britannica, 

 where the use of Reciprocal Figures as a practical method in Graphic 

 Statics is again explained, with the advantage of the simplified system 

 of lettering introduced by Mr. R. H. Bow.] 



After discussing a great variety of examples, the author points 

 out the advantages which the method of reciprocal figures has over 

 graphic processes formerly in use and over algebraic methods of 

 calculating stresses, and concludes by repeating that the merit of 

 discovering the method is entirely due to Professor Maxwell and 

 Mr. Taylor, the object of his paper having been to put the theory in 

 a form intelligible to the engineer. 



XXVII. On Braced Arches and Suspension Bridges. 'Transactions 

 of the Royal Scottish Society of Arts,' 1870, vol. viii. 



The author explains the difference between an ordinary beam or 

 bridge-frame, in which the reactions of the supports are vertical, and 

 a braced arch or braced suspension bridge, in which the forces at the 

 supports are indeterminate until account is taken of the stiffness of 

 the rib and yield of the abutments. He had perceived in 1861 that 

 the true form of a stiff rib or stiff chain would l>e that in which two 

 members would be braced together like the top and bottom members 

 of a girder ; that in the arch both members might be in compression, 

 and in the chain both might be in extension, whereas in a girder 

 one is compressed and one extended. He had found, however, that 

 he was unable to calculate, except on unproved assumptions, the 

 distribution of stresses, being unable to find the force at the sup- 

 ports. He drew Professor Clerk Maxwell's attention to the problem, 

 and Maxwell published ('Phil. Mag.,' May 1864) a method by which 

 all stresses in framed structures could be positively determined. 

 Professor Jenkin then gives an abstract of the method, which is based 



