312 Intelligence and Miscellaneous Articles. 



essential to the successful practice of his system*. He altered another 

 old engine at Wheal Unity, by adding a small cylinder to it ; the per- 

 formance was improved in about the same degree as that of the old 

 engine with one cylinder. 



In 1816 an entire new engine was made at Dolcoath mine, by 

 Messrs. JefFery and dibble, to work with high-pressure steam acting 

 expansively on Mr. Woolf's system, in one cylinder of seventy-six 

 inches diameter ; it answered extremely well, although it never did so 

 much as the engines with two cylinders had done, whilst they were new 

 and in good order : but as they materially fell off in 1 SI 7 and 1818, 

 when they got out of order, and as the Dolcoath engine kept up to a 

 steady performance of about forty millions, the use of one cylinder for 

 Mr.Woolf s system obtained the preference ; and in a short time after 

 Mr. Woolf's patent expired, most of the old Boulton andWatt's engines 

 in Cornwall were altered to work by high-pressure steam on his sy- 

 stem : some few had an extra cylinder added, but commonly the old 

 cylinder was retained. The advantage of the change from low-pres- 

 sure to high-pressure steam, on Mr. Woolf's system, was manifest 

 in all cases ; but it was greater or less, according as the steam was 

 used stronger, and with more or less expansive action. 



All the new engines since erected in Cornwall have been made ex- 

 pressly to work on Woolf's system, and always with one cylinder, 

 excepting one instance of two cylinders. In 1820 Mr. Woolf made 

 two engines for the Consolidated mines, each with one cylinder ninety 

 inches diameter ; but as neither of those, nor the Dolcoath engine, 

 ever did so much as the engines with two cylinders had done at first, 

 Mr. Woolf still felt inclined to prefer his original plan. Accordingly 

 in 1824, having undertaken to make two large engines at Wheal 

 Alfred, he prevailed on the adventurers to go to the expense of 

 making one of them with two cylinders, of forty and seventy inches 

 diameter, the other engine being the same as those at Consolidated 

 mines, with one cylinder ninety inches diameter ; both engines were 

 worked with high-pressure steam. The performance in 1825 aver- 

 aged 4001 millions with two cylinders, and 42*15 with one cylinder: 

 this was considered decisive against two cylinders f ; and no engines 

 have since been made in Cornwall either by Mr. Woolf or others, 

 except with one cylinder, to work on his system. 



The performance of those engines was very slowly and gradually 

 increased, as appears by the following annual averages of the highest 

 performances that are to be found amongst them each month. Until 

 1826 their performance remained below that of the first engines with 

 two cylinders in 1816, which then averaged46*97 millions. Previous 



* The same fact had been ascertained years before, in respect to Mr. 

 Watt's system of working expansively by low-pressure steam; for Mr. 

 Hornblower, who practised that system in two cylinders, did not succeed so 

 well as Mr.Watt himself, who only used one cylinder. 



f The engine with two cylinders had boilers on a complicated plan which 

 did not answer well, and the other engine had very good boilers. If both 

 engines had been worked with equally good boilers, the two cylinders would 

 have made the best performance. 



