SCIENTIFIC SUMMARY. 
93 
Artificial Stone . — An interesting article will be found in Engineering , Get. 
22, on Coignet’s “ B6ton agglomere,” which has come into extensive use in 
France, as most engineers will know. This Beton is a mixture of a large 
amount of sand with a small proportion of lime and cement. The propor- 
tions vary according to the quality of the sand and the rapidity required in 
setting. In many of the works in Paris five parts of sand, one of lime and £ 
to ^ of cement have been used. The mixture is made with the least quan- 
tity of water capable of forming a paste, in a grinding mill, and when 
moulded into blocks in moulds is subjected to compression by heavy blows. 
The result of the small quantity of water used, the thorough mixing, and 
compression, is a material of much greater strength, density, and uniformity 
of character than ordinary concrete. In Paris forty miles of sewers have been 
constructed of this material. At Verinet a church, which is a complete 
monolith, has been similarly constructed. It has also been used for railway 
arches, aqueducts, tunnels, and other structures. 
Communication with the Continent . — At the Society of Arts a paper has 
been read by Mr. Zerah Colburn, and at the Society of Engineers one by 
Mr. Nursey, on the important subject of communication between this 
country and France. 
Steam Brake . — With the progressive increase of the power of the modern 
locomotive, and consequently of the weight of railway trains, it has become 
a question of the greatest importance to find means of controlling the trains 
after having been put in motion. It has been the practice in extreme emer- 
gencies to retard the train by reversing the engine ; when that is done, the 
hot air passing up the chimney is drawn down the blast-pipe and pumped 
into the boiler against the steam pressure, and a very powerful retarding 
force is consequently obtained. But the reversed working is dangerous. 
The heated air drawn into the cylinders burns the lubricant, and the 
particles of soot soon cause serious cutting of the rubbing surfaces. It has 
occurred to a French engineer, M. Lechatelier, to arrange the engine so that 
the link motion may be reversed without danger to the engine, and the 
powerful retarding force supplied by the cylinders, when acting as pumps, 
may be used in the ordinary working of trains. This he effects by introduc- 
ing a small jet of hot water from the boiler into the base of the blast-pipe. 
The water generates at once a large volume of steam, which, in the reversed 
action of the engine, is drawn into the cylinders in place of the heated pro- 
ducts of combustion. Mr. Siemens, in an interesting paper on this brake, 
read at the Institution of Mechanical Engineers, states that this plan of 
working has been adopted on 1,400 locomotives on the Paris and Lyons Rail- 
way alone. It is being introduced in this country by the Fairlie Engine 
Company. 
Velocity of Shot and Pressure of Gases in the Bore of Guns . — Captain 
Noble has invented and applied a remarkable apparatus by which the pres- 
sure of the gases and the velocity of shot within the bore of a gun can be 
measured, at any number of points during its passage. For measuring the 
velocity, the apparatus consists of a mechanical arrangement for obtaining a 
very high velocity of a recording surface, and of an electrical arrangement 
for registering upon the surface the exact instants at which the shot passes 
each point in the bore of the gun. The details of the instrument are too 
