341 
Steam Engifie„ 
main cylinder, should be larger than the lower ones, it 
being the reservoir as it were into which the lower ones 
send the steam, to be thence conveyed away by the steam 
pipe or pipes. The following general direction may be 
given respecting the quantity of water to be kept in a 
boiler on my construction it ought always to fill not 
only the lower tubes, but the main cylinder A and the 
cylinder C to about half their diameter; that is, as high 
as the fire is allowed to reach — and in no case ought it to 
be allowed to get so low as not to keep full the necks or 
branches which join the smaller cylinders, marked with 
the letter a, to the cylinders A or C ; for the fire is only 
beneficially employed when applied, through the medium 
of the interposed metal, to water, to convert it into steam : 
that is, the purpose of my boiler would in some measure 
be defeated, if any of the parts of the tubes exposed to the 
direct action of the fire should present in their interior a 
surface of steam instead of water, to receive the transmits 
ted heat, which must more or less be the case if the lower 
tubes, and even a part of the upper, be not kept filled with 
the liquid. 
“ As to the construction of the furnaces, though that 
must be obvious from the drawings, it may not be im» 
proper here to remark that they should always be so built 
as to give a long and waving course to the flame and heat- 
ed air, or vapour, forcing them the more effectually to 
strike against the sides of the tubes which compose the 
boiler, and so to give out a large portion of their heat be- 
fore they reach the chimney : unless this be attended to, 
there will be a much greater waste of fuel than necessary ; 
and the heat communicated to the contents of the boiler 
will be less from a given quantity of fuel. 
“ My invention is hot only applicable to all the uses to 
which the boilers in common use are generally applied, 
but to all of them with much better effects than the latter, 
Vol. II. X X 
