32 CHAPMAN. 



means of building bridges on the skew principle, in any required 

 situation, without altering the direction of the roads or wasting 

 material, and at an expense little above that of ordinary rectangular 

 bridges. This he accomplished by the principle of building the 

 courses of voussoirs at right angles to the face of the arch, meeting 

 the abutments at oblique angles, being the very reverse of the system 

 previously practised. 



During the progress of the Kildare Canal, Mr. Chapman, at the 

 request of the Duke of Leinster, became overseer, conjointly with 

 him and the Hon. Mr. Ponsonby Moore, for the building a bridge of 

 five arches over the Liffey, to replace the former one which had been 

 carried away by a flood. The bridge itself was a plain structure, 

 but the means employed in forming and securing the foundations 

 attracted general attention, and brought Mr. Chapman into still 

 greater notice. From this time the number and importance of his 

 professional engagements continued to increase, and he was engaged 

 to survey and report upon several projects for the improvement of 

 the navigations of various rivers, of which plans the most important 

 was the navigation of the river Barrow, from Athy downwards. 

 During this period he was appointed consulting engineer to the 

 Grand Canal of Ireland, of which undertaking Mr. Jessop was 

 directing engineer ; and under the joint superintendence and surveys 

 of these two gentlemen, the extension of the Grand Canal from 

 Robarts Town to Tullamore was laid out, as well as the Dock be- 

 tweenDublin and Ringsend, and thecanal of communication by the line 

 of the circular road. The projected canal from near Tullamore passed 

 through extensive bogs, some of which were thirty feet in depth, 

 and in consequence of its difficulties was laid out by Mr. Chapman 

 himself. The directors of the Grand canal had expended upwards 

 of 100,OOOZ. in a very short space of ground between Robarts Town 

 and Bathangar, from not being acquainted with the extent of the 

 subsidence of bogs under superincumbent weight, or when laid dry 

 by drainage. Mr. Chapman, therefore, availed himself of their dearly 

 bought experience, and adopted the following ingenious method of 

 comparing different kinds of bogs and their relative subsidence. He 

 provided himself with a cylindric implement of steel plate, sharp 

 at the lower edges, and containing exactly one hundredth part of a 

 cubic foot, and having divided the strata of the bogs into as many 

 leading classes and subdivisions as were necessary, he filled the 

 cylinders with a specimen of each, by twisting them round so as to 

 cut the fibres of the bog. The samples thus taken were carefully 

 cut off at the level of the cylindric guagc, and their weight having 

 been ascertained, they were left to dry during the space of several 

 months ; and when in a firm state and consequently greatly con- 

 tracted, were again weighed, the result being that the originally 

 wettest bog was found to have lost 10-llths of its weight, and the 

 firmest 2-3rds, the rest in due progression between. Ittherefore 



