THE CORNISH PUMPING ENGINE. 
25 
the Paper referred to, and the duty of these atmospheric engines has been found 
= 7,037,800 lbs. lifted one foot high by a bushel of coals. 
The performance of every engine used under the patent was carefully compared 
with the standard thus settled, and the patentees’ remuneration determined ac 
cordingly. 
It will be remarked that this standard was derived from the duty of the old 
atmospheric engine, excluding the effect of the improvements of Smeaton, by which 
40 or 50 per cent, more duty had been obtained. 47 This circumstance was after 
wards brought forward as a ground of complaint against Messrs. Boulton and Watt, 
but it cannot be denied that the miners were, equally with the patentees, parties to 
the agreement by which the latter were to be remunerated. 
i 
37. For greater convenience in computing the performance of his engines, Watt 
introduced the method of estimating it which has continued in use to the present 
time, and which consists in determining what is denominated the duty. 
The meaning of this expression, in general terms, may be stated to be, the amount 
of work done, or useful effect produced, by an engine, considered in proportion to the 
quantity of fuel expended. In its practical application it is understood to refer to 
the number of pounds weight lifted one foot by the consumption of one bushel 48 of coal. 
Thus when it is said that a certain pumping engine performs a duty of forty 
millions, it is understood to mean that the engine lifts forty millions of pounds of 
water one foot high, or what is equivalent to this, for each bushel of coal consumed. 
So by finding the quantity of water raised by each stroke of the engine to a 
certain height, taking the number of strokes made in a given time, by the aid 
of the counter (an instrument also invented by Watt for the purpose 49 ), and ascer 
taining the number of bushels of coal burnt during that time, it becomes an easy 
matter to express the duty of the engine in terms which shall at once designate its 
economical condition, and enable it to be compared with any others whose duty is 
expressed in a similar manner. The word is particularly applicable in tracing the 
progressive improvement of the engine. 
38. It has been already stated that the duty of the two atmospheric engines at 
Poldice, which formed the standard of comparison, was about seven millions. This 
47 Mr. Watt says, in a letter to Smeaton, “ In all these comparisons, our own interest makes us except 
your improved engines, unless we were allowed a greater proportion of the savings.” 
48 A bushel of Welsh coal is now estimated to weigh about 94 lbs., and this is the weight to which the 
duty as now reported is supposed to refer. See the articles on coal and duty in the descriptive part of this 
work. 
49 See Farey on the Steam Engine, page 520, for a description of this machine. 
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