214 
POPULAR SCIENCE REVIEW. 
these consists of a massive timber framing, carrying a sort of gigantic cut- 
water and mould-board. Driven by five or six luggage engines, this plough 
will clear a way through drifts 10 or 11 feet deep at the rate of 25 miles per 
hour. Dor smaller drifts a medium sized plough is used attached to a pilot 
engine running in front of the trains, when occasion requires ; and during the 
winter each engine is fitted with a still smaller plough, not rising above the 
buffer beam of the engine but capable of doing good service in drifts of 2 or 
3 feet deep. 
Safety Valves . — We need not fear that the sphere of mechanical research 
is exhausted, when so simple a matter as an ordinary safety valve still re- 
quires and rewards investigation. Mr. Thomas Baldwin has communicated 
to the Society of Engineers some very interesting experiments on the dis- 
charging power of safety valves, or the influence of the form of the valve on 
the lift of the valve for any given excess of pressure in the boiler over the 
weight with which the valve is loaded. The valve employed in the experi- 
ments was one inch in diameter, and was fixed in the manhole lid of an or- 
dinary two-flued boiler. The following are some of the results. 
Pressure in Boiler Weight on valve in lbs per sq. in. 
Valve in lbs. per sq. in. in- when the valve lifted the under men- 
cluding atmosphere tioned fractions of its diameter. 
J_ ±_ 8 12 16 
80 80 80 80 80 
A . 
. . 65 
. 58± 
53i 
52± 
51* 
D 
. 65 . 
, . 53^ 
49± 
48f 
48 
L . 
. 67 . 
. 56i 
52 
49* 
48.i 
M . 
. 67 . 
45 
Valve A a disc valve, guided by outside pins j D, disc valve with inside 
wings ; L, ordinary conical valve with 3 wings, and seat § in. wide ; M, disc 
valve 1| in. diam. 
These experiments show that we cannot have the ordinary valve of suffi- 
cient area to allow the steam as rapid an exit as it ought to have unless the 
valves be very large. Mr. Baldwin proposes a spherical valve with a pro- 
jecting seating, so arranged, that when the valve opens, the steam acts on a 
larger area of the valve than when shut. Such a valve If inch diameter he 
considers twenty times as effective as a disc valve five times its diameter. 
Casting Steel under pressure. — Mr. Whitworth has invented a system of 
steel casting under enormous hydraulic pressure, with a view to produce a 
material of more uniform and ductile quality, and requiring less subsequent 
hammering or rolling. Steel shot of satisfactory quality have already been 
produced and the process i3 to be extended to the manufacture of ord- 
nance. 
Turret Ships . — A very important discussion has taken place at the Insti- 
tute of Civil Engineers on the American Monitor system which has found a 
most able and competent advocate in Mr. John Bourne. There appears to 
be little doubt that additions to our Navy will be made, in which a modifi- 
cation of Capt. Coles’s and Ericsson’s plans will be adopted, and which will 
carry armour 15 or 16 ins. thick and 20-ton guns. In these the hull will 
follow the Monitor type, with its low deck almost level with the water, but 
the turrets will be carried up through a raised breastwork rising 7 to 10 feet 
above the deck. 
