Report on the Progress and State of Applied Mechanics. 217 



of the same cast iron asunder directly. Mr. Bai-low calls tlie additional 

 resistance which he has discovered, resistance of flexure, and has 

 framed an ingenious theory of the manner in which it is produced. It 

 is possible, however, that it may arise altogether from the superior 

 strength of the skin of the iron, as compared with that of the interior of 

 the mass ; for experiments on direct tension show the tenacity of the 

 interior, in the very centre of the mass, where it is weakest, while 

 experiments on the cross-breaking of beams show the tenacity of parts 

 of the mass, either at or near the skin. But be the cause of the addi- 

 tional resistance what it may, its discovery is one of the highest impor- 

 tance. It is described in two papers, published in the Philosophical 

 Transactions for 1856 and 1857. 



41. Dr. AVilliam Thomson, in the course of the present year, with 

 the assistance of two students of his class, discovered a kind of resis- 

 tance in elastic solids, analogous to friction, inasmuch as it retards, 

 without finally preventing, both the strain produced by the application 

 of a load, and the recovery from that strain when the load is removed. 



42. The PROCESSES oe CoNSTnucTioir, employed in the making of 

 structm'es, depend on the nature of the material, and may be classed 

 into Earthvjork, Masonry, Carpentry, and Metal-work. 



43. The unparalleled magnitude of the Eaethwoeks, including 

 excavations, embankments, shafts, and tunnels, required for the Rail- 

 ways, which for more than a quarter of a century have been extending 

 over the world, have naturally led to an increase of skill in the practical 

 details of the operations by which they are executed ; but it would be 

 difficult to point out many specific inventions by which those operations 

 have been improved, except some ingenious machines for digging earth 

 and tunnelling in rock, which have been introduced to a limited extent. 

 It may be mentioned as an interesting fact, that the cost of the ordinary 

 earthwork of Railways, per cubic yard, is nearly the same all over the 

 world, the differences in the wages of the excavators being compensated 

 by the differences in their efficiency. For example, it is stated, that on 

 the East Indian Railway, where the excavators' wages are about one- 

 twelfth of the wages in Britain, twelve times as many excavators are 

 required to do the same quantity of work, and the result is, that the 

 cost of the earthwork is nearly equal in both regions. 



44. Connected with the subject of eai'thwork, is that of foiwda- 

 TIOKS. The gradual extension of the use of concrete, in foundations on 

 soft ground and under water, has already been referred to. A useful 

 method of making foundations for heavy structures, such as viaducts, 

 on soft ground, of great depth, is to sink cylindrical wells, lined with 

 brickwork or ashlar masonry, resting on a drum-curb, which is lowered 



Vol. IV.— No. 1. 2f 



