80 POLE STEAM-ENGINE. 



Cainborne locomotive, the pole steam-engine, were all 

 built on the same groundwork originally started with, 

 of greatest simplicity of form, and absence of many 

 pieces ; and it may be observed that he never applied 

 for a patent until the value of the idea had been proved 

 by experiment. 



In practice the difficulty of keeping the pole-packing in 

 order was one of the objections to the plan ; for it either 

 leaked, or, if packed tight, caused much friction and 

 wearing away of the middle of the pole faster than the 

 ends, from the greater speed at the middle of the stroke. 

 The steam-ring was therefore of importance in the 

 engine, in those days of inaccurate workmanship ; like 

 the water cup on the gland of the plunger-pump packing, 

 it prevented external air from injuring the vacuum. 



" MR. GlDDY, " CAMBORNE, July $th, 1815. 



"Sir, About a fortnight since I received letters from 

 Lima, and also letters to the friends of the men who sailed 

 with the engines. They arrived on the 29th January, after a 

 very good passage, and without one hour's sickness. Both their 

 and my agreements were immediately ratified, and they are in 

 high spirits. The ship finished discharging on the llth Febru- 

 ary, which was the day those letters sailed from Lima with 

 $12,000 for me, which has all arrived safe. 



"I shall make another fit-out for them immediately. I 

 expect that all the engines will be at work before the end of 

 October; half of them must be at work before this time. The 

 next day, after their letters sailed for Europe, they intended to 

 go back to the mines. Woolf 's engine is stopped at Herland, 

 and I have orders to proceed. A great part of the work is 

 finished for them, and will be at work within two months from 

 the time I began. I only engage that the engine shall be equal 

 to a B. and Watt's 72-inch single, but it will be equal to a 

 double 72-inch cylinder. It is a cast-iron plunger-pole, over the 

 shaft, of 33 inches diameter, 10-feet stroke. The boiler is two 



