6 
POPULAR SCIENCE REVIEW. 
surprising^, then^ that every means have been employed to get 
high steam-power in the cigar-ship and that instead of 
her engines working like the Gh'eat Eastern at 25 lb. pressure, 
they will be worked at 150 lb., or even 180 lb. to the 
Fig. 12.— The Great Eastern. 
square inch. An important improvement, too, has been 
made in the arrangement of the tubes of the vertical 
boilers with which she is furnished, in respect to the 
central portion being left open for the down current of 
the water during the ebullition, while the upper part is freely 
open for the superheating of the steam. This open central 
space permits also the cleansing off of the saline deposits from 
the evaporated water which encrust the tubes, an operation 
impossible in ordinary tubular boilers, which consequently 
suffer greatly from corrosion. 
There may be some slight gain of cubical dimensions by the 
cigar-ship from the difference in the form of her hull over 
that of an ordinary vessel, as we may see by superposing the 
diagram of the vertical midship section of the one over the 
other, as in fig. 13, in which both 
sections have the same length of 
boundary, and would, therefore, re- 
quire the same amount of material 
to inclose them. But there is no 
such difference as should give space 
for any remarkably disproportionate 
quantity of steam-power. Working* 
the engines at a higher pressure 
is simply putting more steam-power 
in the same amount of space ; and if 
there were no difference of limits 
put by mere size on the pressure the 
boilers of the biggest ship would bear, there is no other reason 
Fig.13.— Superposed Midship Sections 
of “ Cigar-ship ” and Ordinary Ship. 
