MAGAZINE OF SCIENCE AND AET. 
213 
their inferiority to those of Trevithick in favor of ; 
which they were soon relinquished. Previously to 
Mr. Woolf’s coming into Cornwall, he had revived 
Mr. Hornblower’s idea of employing the expansive 
force of steam in a second cylinder, and he suc¬ 
ceeded in obtaining from engines of that construc¬ 
tion a much better performance than had yet been 
effected by Mr. Watt’s engines, and in 1814 the 
duty was advanced to 54 millions. During a period 
of six years, namely, from 1814 to 1820, Woolfs 
double cylinder maintained its superiority, and its 
average duty was very far beyond that of Watt's 
engines, then at work in the neighbourhood. In 
1815, the effects of some of Woolfs engines were 
brought into direct comparison with those on Mr. 
Watt’s expansive principle, and a statement of their 
performance was periodically published. 
One of these engines which worked at Huel 
Abraham mine, during a trial which was continued 
for 24 hours, lifted 70 millions of lbs. 1 foot high 
by the combustion of one bushel of coal, shewing 
an immense difference in the effect of the engines 
of Mr. W'aft and Mr. Woolf, the difference being 
in Mr. Woolfs favour. The adventurers in mines 
and the Cornish engineers now began to see tlic 
important advantages to be derived from using 
steam expansively, at a much higher initial pres¬ 
sure than was used in Mr. Watt’s engines. The 
theory of combustion was not in those days so 
generally and accurately understood as it is at pre¬ 
sent, and the fires in Mr. Watt’s engines were of 
much larger dimensions than experiments now con¬ 
firmed by more extensive experience have demon¬ 
strated to he most consistent with economy of fuel. 
The ordinary consumption of fuel in one of Boul¬ 
ton and Watt’s engines is stated by Mr. Russell to 
he 10 lbs. of coal for each horse per hour, whereas 
in the Cornish high pressure expansive and con¬ 
densing engine, the consumption of coal is only 21 
lbs. per h.p. per hour. The difference, or 7| lbs. 
of coal per h.p, per hour, represents therefore the 
superior economy and efficiency of the Cornish en¬ 
gine, when constructed in the best manner, and 
places this form of engine in the first rank; so that 
for effectually performing its work at great depths, 
and for the small comparative amount of fuel con¬ 
sumed by it, the Cornish pumping engine stands 
unrivalled. 
Great, then, as were the advantages which fol¬ 
lowed the introduction of Wyatts’ first engines in 
Cornwall, they have been exceeded by the im¬ 
provements which have been effected in the steam- 
engine since his time ; so that it is a fallacy to say 
that “ The history of the steam-engine ends with 
the history of Mr. Watts’ labours.” The writer 
would be sorry to be considered as being actuated 
by the mere desire of commenting unnecessarily 
upon what he considers a fallacious statement, or 
of being actuated by the desire of detracting from 
the fame of so deservedly great a man as James 
Watt; hut he considers it a duty which he owes to 
the profession to which he has the honour to be¬ 
long, to analyse carefully every statement which 
may appear of doubtful accuracy, and particularly 
when such a statement is made in a work professing 
to give an impartial account of the steam-engine. 
We five in an age of change and progress, and 
nothing \s more calculated to limit our knowledge 
of cause and effect than to give our blind assent to 
dogmas of doubtful truth, even although they may 
he generally received as true. In the year 1834 
the duty of the Cornish engines amounted to 90 
millions of pounds, and since that time it has con¬ 
tinued to increase in the ratio of 90, 100, and 110 
millions; and in 1S40 Mr. Taylor reported, at a 
meeting of the British Association, that the duty 
of the Cornwall engines amounted to the unequal¬ 
led performance of 123,300,593 lbs.! 
From the above facts it cannot he doubted that 
the improvement in steam-engines lias been pro¬ 
gressive, and that, however much may have been 
hitherto done, it is impossible to state confidently 
that even now the whole inherent power residing in 
one pound of coal, or other fuel, is rendered 
available. 
The saving effected in the consumption of fuel 
is a matter of deep importance, even in countries 
where coal is cheap; hut where it is not so it be¬ 
comes a matter of vital importance not only to the 
manufacturer but to the whole community. 
In Cornwall tlic improvements effected in the 
steam-engine soon enabled the mines to he worked 
to a depth previously considered unattainable, and 
laid the foundation for further improvements; so 
that at fhe present time it may be said that there is 
practically no limit to the depth attainable in the 
mines of that county ; a shaft m the consolidated 
mines having been carried to the enormous depth 
of 330 fathoms, or 1980 feet perpendicular! 
In order fully to understand wherein the Cornish 
pumping-engine differs from t ie usual form of 
the Boulton and Watt single-acting engine, it will 
be necessary to institute a comparison between the 
two. It will then be seen that the chief points of 
difference are as follows:— 
First. In. the Cornish form of boiler the steamer 
is raised to an absolute pressure, varying from 30 
to 40 and 50 lbs. on the square inch, and some¬ 
times it is even carried as high as 60 lbs., whereas 
in the waggon-headed boiler in general use for a 
Boulton and Watt engine, the absolute pressure of 
the* steam seldom exceeds IS or 20 lbs. to the 
square inch. This form of boiler, in fact, is not 
calculated to sustain any greater pressure, being 
inherently weak, and requiring to be well stayed in 
the inside, as a very small pressure has been found 
sufficient to bulge these boilers downward towards 
the fire, and outwards at the sides. 
Secondly. The steam is cut off in the cylinder of 
the Cornish engine when the piston has travelled 
l-3rd, l-4th, l-5th, 1-6‘th, or even l-8th part of 
the stroke, and the full advantages of expansion 
are obtained ; whereas, in the ordinary form of the 
Boulton and Watt engine the steam is seldom shut 
off before the piston has made 3-4ths, or a larger 
proportion of the stroke. In fact, it is useless to 
attempt to expand low pressure steam, for the 
simple reason that there is nothing to expand. 
Thirdly. In the Cornish engine steam is ad¬ 
mitted into the jacket of the cylinder by means of 
a separate pipe, and the condensed steam returns 
through another pipe into the boilers, which latter 
are placed sufficiently low down with regard to the 
cylinder to effect this drainage; whereas, in the 
common form of the Boulton and Watt engine, the 
same pipe which supplies the cylinder supplies also 
the jacket, and the condensed steam is not returned 
into the boiler, hut is let off by means of a syphon, 
tube, or other contrivance. 
Fourtli. Radiation of heat is almost completely 
prevented in the Cornish system by a wood or 
brick casing surrounding the cylinder, and by 
clothing the steam-pipe and boilers. The latter 
are more frequently covered with a layer of from 
