522 



THE STEAM-ENGINE. 



boiler, nor, with the necessary degree of precision, of the quantity and pres- 

 sure of the steam which passed through the cylinders, this estimate must be 

 regarded as an approximation subject to several causes of error. The ques- 

 tion of the duty of boilers and engines applied to the general purposes of man- 

 ufactures and navigation, is one which has not yet been satisfactorily investi- 

 gated ; and it were much to be desired that the proprietors of such engines 

 should combine to establish a strict analysis of their performance in reference 

 to their consumption of fuel, their evaporation of water, and their useful effects. 

 The results of such an investigation, if properly conducted, would perhaps tend 

 more to the improvement of the steam-engine than any discoveries in science, 

 or inventions in mechanical detail, likely to be made in the present stage of 

 the progress of that machine. 



A strict investigation of this kind has been for many years carried on re- 

 specting the performance of the steam-engines used for the drainage of the 

 mines in Cornwall ; and it has been attended with effects the most beneficial 

 to the interests of those concerned in them. The engines to which this im- 

 portant inquiry has been applied being used for the purpose of pumping, are 

 generally single-acting engines, in which steam is used expansively to a great 

 extent. The steam is produced under a very high pressure in the boiler, and 

 being admitted to the cylinder is cut off after a small portion of the entire 

 stroke has been made, the remainder of the stroke being produced by the ex- 

 pansion of the steam. 



About the year 1811. a number of the proprietors of the principal Cornish 

 mines agreed to establish this system of inspection, under the management 

 and direction of Captain Joel Lean, and to publish monthly reports. In these 

 reports were stated the following particulars : 1, the load per square inch on 

 the piston ; 2, the consumption of coal in bushels ; 3, the number of strokes 

 made by the engine ; 4, the length of the strokes in the pumps ; 5, the load in 

 pounds ; 6, the duty of the engine, expressed by the number of pounds raised 

 one foot high by the consumption of a bushel of coals ; 7, the number of 

 strokes per minute ; 8, the diameter and stroke of the cylinder, and a general 

 description of the engine. When these reports were commenced, the number 

 of engines brought under inspection was twenty-one. In the year 1813, it 

 increased to twenty-nine ; in 1814, to thirty-two ; in 1820, the number report- 

 ed upon increased to forty; in 1828, the number was fifty-seven; and in 

 1836, it was sixty-one. This gradual increase in the number of engines 

 brought under the system of inspection, was produced by the good effects 

 which attended it. These beneficial consequences were manifested, not 

 only in the improved performance of the same engines thus reported upon, 

 but in the gradually-improved efficiency of those which were afterward con- 

 structed. 



The following table, taken from the statement of the duty of Cornish en- 

 gines, will show in a striking manner the improvement of those engines, 

 from the commencement of this system of inspection to the present time. 

 The duty is expressed by the number of pounds raised one foot high by the 

 consumption of a bushel of coals. 



As an example of the beneficial effects produced upon the efficiency of an 

 individual engine by the first application of this system of inspection, the 

 case of the Stray Park engine may be mentioned. This engine, constructed 

 by Boulton and Watt, had a sixty-inch cylinder, and when first reported in 

 1811, its duty amounted to 16,000,000 pounds. After having been reported 

 on for three years, its duty was found to have increased to 32,000,000 ; this 

 estimate being taken from the average result of twelve months' performance. 

 Its duty was doubled in less than three years. 



