4& AGRICULTUKAL ENGINES. 



in conjunction with the mules in the same mill at the same 

 time. 



" To inform your friend of the power and effect of such an 

 engine, I prefer his sending some person down to Cornwall, to* 

 see it tried on some of the cattle mills or whims in the mines. 



"Engines that have been sent to the West Indies hitherto 

 have cost nearer 2000?. ; very large, heavy, and complicated 

 machines, requiring 2500 gallons of water per hour for con- 

 densing,, and could only be managed by a professed engineer, 

 while any common labourer can keep in order and work these 

 engines. If you prefer to send a person with it, the cost will 

 be about 40s. per week. 



" I remain, Sir, 



u Your most obedient servant, 



u RICHAKD TREVITHICK." 



This letter indirectly points out two long-standing 

 radical errors in engineering phraseology. An early 

 method of describing the value of. an engine was by 

 stating the number of pounds it would lift one foot 

 high by the burning a bushel of coal, called the duty 

 of an engine. Trevithick's bushel was 84 Ibs., while 

 other engineers, under the same term of bushel, meant 

 various weights, up to 120 Ibs. 



Another form of speaking was the horse-power of an 

 engine ; meaning that a horse could lift a certain 

 number of pounds one foot high in a minute, and that 

 a steam-engine lifting ten times as much was a 10- 

 horse engine ; but, as Trevithick points out, a horse 

 only works at that rate for six hours out of twenty- 

 four, while the steam-engine works continuously, per- 

 forming the work of forty horses, yet is called a 10-horse 

 engine. 



The higb -pressure engine suitable for the West 

 Indies was to be adapted to the existing horse or mule 



