34 VARIOUS INVENTIONS. 



An engine of 4-horse power will not require a space of more 

 than 5 feet high, 5 feet long, and 3 feet inches wide. In some 

 instances I employ a balanced wheel 5 feet in diameter. The 

 water required will be a pint and a half per minute. The coal, 

 one quarter of a bushel or 21 Ibs. per hour. The price of a 

 machine, finished and set to work, 100 guineas. It does not 

 require either wood or mason work, but stands independent of 

 every fixture, and may be set to work in half an hour after being 

 brought on your premises. 



" Your obedient servant, 



" KICHD. TBEVITHICK. 



" DR. MOORE, M.D., Exeter." 



A 4-horse-power portable high -pressure steam-puffer 

 engine cost 105/., with internal fire-tube and machinery 

 attached to the boiler, ready for work in half an hour 

 after lighting the fire, consumed 21 Ibs. of coal and 

 11 gallons of water for each hour's work, at a cost of 

 threepence. 



The reader's attention has been very imperfectly 

 drawn to the numerous subjects touched on in these 

 remnants of Trevithick's correspondence between the 

 years 1804 and 1816 ; among them may be traced the 

 portable high-pressure steam-engine, the tubular cylin- 

 drical boiler of wrought iron, the economy of expan- 

 sive working with steam of 100 Ibs. on the inch, but 

 limiting it to 20 Ibs. when not in the charge of expe- 

 rienced workmen, and testing boilers by water pressure 

 to four times the intended working pressure. 



The economy of heat in smelting furnaces and in the 

 aerated steam-engine were bold means to large results. 

 The cheap 100. steam-engine of 1812, with open-top 

 cylinder arid rigid simplicity of gear, resembling New- 

 comen's first atmospheric engine, was really a high- 

 pressure steam expansive engine, with the germ of 



