A careful perusal of M. Nansouty’s memoir leaves us in much doubt as to what M. Estrade’s views are based on.  So far as we understand him, he seems to have worked on the theory that by the use of very large wheels the rolling resistance of a train can be greatly diminished.  On this point, however, there is not a scrap of evidence derived from railway practice to prove that any great advantage can be gained by augmenting the diameters of wheels.  In the next place, he is afraid that he will not have adhesion enough to work up all his boiler power, and, consequently, he couples his wheels, thereby greatly augmenting the resistance of the engine.  He forgets that large coupled wheels were tried years ago on the Great Western Railway, and did not answer.  A single pair of drivers 8 ft. 3 in. in diameter would suffice to work up all the power M. Estrade’s boiler could supply at sixty miles an hour, much less eighty miles an hour.  On the London and Brighton line Mr. Stroudley uses with success coupled leading wheels of large diameter on his express engines, and we imagine that M. Estrade’s engine will get round corners safely enough, but it is not the right kind of machine for eighty miles an hour, and so he will find out as soon as a trial is made.  The experiment is, however, a notable experiment, and M. Estrade has our best wishes for his success.—­The Engineer.

* * * * *

CONCRETE.[1]

   [Footnote 1:  Read July 5, 1887, before the Western Society of
   Engineers.]

By JOHN LUNDIE.

The subject of cement and concrete has been so well treated of in engineering literature, that to give an extended paper on the subject would be but the collection and reiteration of platitudes familiar to every engineer who has been engaged on foundation works of any magnitude.  It shall therefore be the object of this communication to place before the society several notes, stated briefly and to the point, rather as a basis for discussion than as an attempt at an exhaustive treatment of the subject.

Concrete is simply a low grade of masonry.  It is a comparatively simple matter to trace the line of continuity from heavy squared ashlar blocks down through coursed and random rubble, to grouted indiscriminate rubble, and finally to concrete.  Improvements in the manufacture of hydraulic cements have given an impetus to the use of concrete, but its use is by no means of recent date.  It is no uncommon thing in the taking down of heavy walls several centuries old to find that the method of building was to carry up face and back with rubble and stiff mortar, and to fill the interior with bowlders and gravel, the interstices of which were filled by grouting—­the whole mass becoming virtually a monolith.  Modern quick-setting cement accomplishes this object within a time consistent with the requirements of modern engineering works; the formation of a monolithic mass within a reasonable time and with materials requiring as little handling as possible being the desideratum.