SCIENTIFIC SUMMAEY. 
519 
the feed-water. Under the first head, the dynamical action of the steam, 
exerting impnlsive strains on the boiler, is insisted on. The remarkable phe- 
nomenon knoAvn as furrowing is traced to cross-bending action, arising most 
frequently from lap-ri vetted joints. Under the second head, the relative heat- 
transmitting power of thick and thin plates is discussed, the verdict being 
decisively in favour of the latter, and several instances of deterioration are 
traced to imperfect conduction from excessive thickness of the plates. The 
influence of heat in reducing the ultimate strength of iron is considered, and 
it is suggested that there is a thermal elastic limit beyond which, after dilata- 
tion of volume, iron does not return to its original dimensions. This dilata- 
tion is compared with elongation by strains in excess of the elastic limit, and 
is suggested as the explanation of the phenomena of “ burnt ” iron. The 
action of the flame is described as causing the combination of sulphur and 
oxygen with the surface of the plates. The subject of internal and external 
corrosion is treated, with special reference to the peculiar form known as 
“ pitting and, finally, legislative enactments and the hydraulic test are 
discussed. 
Competitive Guns at Shoeburyness . — The following table gives the results of 
the trials of the 7-inch guns alluded to in our last : — 
Elevation. 
Name of 
Gun. 
Mean Range 
in Yards. 
Mean 
difference of 
Range in 
Yards. 
Mean 
reduced, 
deflection in 
Yards. 
2 degrees. 
French 
1,386 
35-4 
0-6 
2 degrees. 
Scott 
1,462 
21-5 
0-9 
2 degrees. 
O 
Lancaster 
1,455 
27-3 
1-9 
Automatic Steering Apparatus. — Dr. J. P. Joule has proposed a method of 
automatic steering by means of a delicately suspended compound system of 
needles or magnetic bars, to the one end of which would be attached a bent 
wire, one of whose extremities would be immersed in a central cup of 
mercury, connected with one of the poles of a voltaic battery, and the other 
would dip in one or other of two concentric semicircular troughs of mercury 
that would be moved round to the right or left, according as the ship would 
turn in one direction or the other. The other pole of the battery would be in 
connection with a branched conductor, leading to two electro-magnets, the 
free wires of which would thus be put in connection with the semi-circular 
troughs, and according as the bent wire Avould be immersed in one or the other 
trough, one or the other electro-magnet would be excited, an armature placed 
between the electro-magnets would be attracted by one or the other of them, 
according as the wire would dip into the one semicircular trough or 
the other. This armature would, by means of levers, &c., open valves, 
which would allow steam to act on one side of a piston or the other, the 
piston being connected with the tiller. By moving round the commutator, 
the shij) may be made to follow any required course. 
