188 
Steam Engine, 
lower temperature than the smaller, its expansibility will 
be lessened ; which, on particular occasions, and for par- 
ticular purposes, maybe desirable. In every case care must 
be taken that the boiler, the case or cases in which the cy- 
linder or cylinders is or are inclosed, the steam pipes, and 
generally all the parts exposed to the action of the expan- 
sive force of the steam, be of a strength proportioned to 
the high pressure to which they are to be exposed. 
With regard to the due degrees of strength of the parts of 
all my said improvements, together with the nature of the 
materials, and the proportions of the same, except as here- 
in described, I forbear any further description, on ac- 
count of the numerous variations to which the same must 
be subjected ; and because every engineer, of sufficient 
skill to be employed in works of this nature, will, with- 
out difficulty, arrange and determine the same accord- 
ing to the nature of the case. 
Lastly. I have to observe, that, to avoid unnecessary 
tautologies in speaking of the proportion that ought to 
subsist between the smaller cylinder or the steam mea- 
sure and the larger cylinder, or the quantity of steam to 
be admitted to the working cylinder, where a separate 
smaller cylinder or steam measure is not adopted, though 
I have mentioned the regular proportions, as, for exam- 
ple, of a measure or quantity equal to one-fortieth of the 
working cylinder when steam of forty pounds the square 
inch is to be employed, or equal to one-thirtieth, or one- 
twentieth, when steam of thirty or twenty pounds the 
square inch is to be used ; yet these are not the only pro- 
portions that may be used ; for, though it may not be ad- 
visable that the proportion of the smaller cylinder or steam 
measure should in any case be made much smaller than 
I have stated, yet, in making it larger, considerable lati- 
tude may be allowed : for example, with steam of forty 
pounds the square inch, a smaller cylinder or measure of 
