TRANSACTIONS OF THE SECTIONS. 211 
and the general use of improved machinery would not fail to produce a corresponding 
improvement in the condition of the agricultural labourer, and to accelerate the com- 
pletion of that progressive revolution, which, since the abrogation of legislative pro- 
tection, has been rapidly taking place in every department of practical agriculture. 
On Double Cylinder Expansion Marine Engines. 
By J. ELDER. 
These engines are constructed with the view of getting the greatest amount of 
power from a given quantity of steam at a given pressure, with less total weight of 
engines, boilers, and water, and occupying less total space than that occupied by the 
ordinary class of steam engines on board steam-ships ; these engines are therefore 
expected to have the following properties :— 
1.—That with these engines a steam-ship can steam the greatest distance pos- 
sible with a given quantity of coals. 
2.—That a given distance can be performed in the shortest time, on account of the 
small weight of coals necessary to be carried. 
3.—That the greatest amount of cargo and passenger accommodation is obtained, 
from the small room occupied by the boilers and coals. 
4.—That where a given capacity of cargo and passenger accommodation is re- 
quired, a smaller and consequently less expensive ship is necessary. 
5.—The boilers, being less than the usual proportion, are less expensive to replace 
when required. 
6.—The number of firemen and stokers is reduced, and, consequently, the space 
occupied by them can be otherwise engaged, and their wages saved. 
To accomplish these objects, the constructors of these engines have followed the 
course we now describe. The cylinder capacity is so great as to admit of the steam 
being expanded to within two pounds of the pressure in the condenser, at the end of 
the stroke, while the engines are working full power. In order to reduce the shock 
of high pressure on such a large piston, a cylinder with a piston one third the size is 
placed close to it. This small cylinder receives the steam direct from the boiler during 
one-third of its stroke, and is then cut off; this steam is consequently reduced to one- 
third of its original pressure at the end of its stroke, and then enters the second 
cylinder, where it is expanded three times more: thus 36lbs. steam is expanded to 
Albs., viz. from 36 to 12 in the first, it then enters the second at 12 and is expanded 
to 4ibs. ; but, as the second piston is three times the size of the first, the load will be 
the same on both pistons, and the piston rods, cross heads, and connexion rods may 
be duplicates of each other. The steam and eduction slide valves are wrought with 
eccentrics. The steam valve is a gridiron with large flap ; the eduction valve, which 
serves for both cylinders, has no lap, and the eduction ports remain open during the 
entire stroke of the piston, thereby giving a free egress for the steam, and ample 
escape for water, should it form. 
In reversing the engines the eccentrics are made to overrun the shaft till they arrive 
at the backing catch—a plan which is less likely to cause accident than the ordinary 
methods, The cylinders are steam-jacketed completely, and then covered with felt 
and wood. There is a small engine pump for forcing the distilled fresh water from 
the jackets into the boilers, or to the fresh-water tanks, if necessary. 
The boilers now being made for such engines are tubular, with three large super- 
heating uptakes, 2 feet in diameter and 15 feet high, leading up through an oval 
steam chest to the funnel; this makes a strong form of take-up, where it joins the 
tube plate, especially in boilers firing across the ship. The feed-pipe of the boilers 
has twelve spiral conyolutions inside the funnel to heat the feed-water. This may 
be shut off when desirable. 
The author then mentions the various vessels in which these engines have been 
fitted, and shows by comparison with other engines the great saving of expense, 
combined with greater efficiency. 
A Description of a Hand Heliostat. By F. Gatton, S.G@.S. 
; By this simple instrument the rays of the sun could be flashed with ease and pre- 
cision upon any required spot, The appearance it produced was that of a brilliant 
14* 
