Notes on Steam Boilers. 327 
more easily cleaned, and repaired than almost any other 
kind, and although like all other good things, they can 
only have their day, the improved boiler that may 
ultimately take their place, does not appear to be 
so far developed as to make steam users hesitate 
in adopting the " Lancashire" or " Cornish", and 
feeling confident as to these giving the best general 
results for a long time to come. A Compound boiler 
is simply a short Lancashire and multitubular connedled 
together, and is, perhaps with clean water and good 
draught the most economical for fuel, being simply a 
cheap way of carrying out the principle of the marine 
boiler, whose economy is most perfect. In it w r e have the 
internal grate, and fire box, which is the most efficient 
kind of heating surface, then the combustion chamber, in 
front of tubes. Mr. WiLSON very clearly points this out 
in his instructive work on boilers ; unfortunately there 
are many practical objections to their working that have 
placed them somewhat out of fashion in this colony, not 
the least of which is their inaccessibility for repairs. 
Design. After deciding as to the type of boiler, and 
power required ; the steam user should be careful to 
ascertain that each part of the structure will be propor- 
tionate. Many boilers, both new and old, are found 
to be very deficient in this respe6l, certain parts having 
an ultimate strength equal to eight or ten times that of 
the working pressure, whilst others have only faftors of 
safety of two, or three, which reminds one of the two 
parts of the ten-ton chain, united by a three-ton link. As 
all the parts of a boiler are of importance, full details 
should be provided for the guidance of the boiler-maker. 
There are certainly many competent firms who make a 
TT 2 
