360 Report on the Exhibition of Implements 



Whitfield, Uth September, 1847. 



Dear Sir, — The opportunity which you gave Mr. Love and myself 

 yesterday of making a thorough examination of Cambridge's portable 

 steam-engine (which you have had for 6 months), and of seeing it in 

 full work for 3 hours, has confirmed our previous opinion of its merits, 

 and of its adaptation to agricultural purposes. 



The "important data," viz. "the diameter of the cylinder and the 

 length of the stroke," which the Council required of us to enable them 

 to settle the question of merit, form, according to my view of the matter, 

 only part of the elements required for measuring the power of a steam- 

 engine. The Great Britain steam-boat had her steam-engines of 1000- 

 horse power according to measurement, but they were never able to 

 work up to 600 horse. The cylinders of the railway locomotive engines 

 are all of the same size, but their power is different, and this difference 

 is neither owing to the diameter of the cylinders nor to the length of 

 the stroke, but to the quantity of water converted into steam per mi- 

 nute at a particular temperature and properly used. 



I have enclosed a diagram of the boiler, the safety-valve, the length 

 of the lever, and the weight of the ball, so that Mr. Parkes may be en- 

 abled to judge of the pressure of the steam. 



The greatest length of the lever is 14 inches; the diameter of the 

 safety-valve is 1^ inches, the weight of the ball is 21^ lbs. ; 90 lbs. per 

 square inch is the greatest pressure when the ball is at the end of the 

 lever; but as the weight on the lever was only 10 inches from the ful- 

 crum while it was worked in our presence, the pressure on the square 

 inch was not quite 60 lbs. 



The time I saw the engine at work (as I have already stated) was 3 

 hours ; it was driving a 6-horse thrashing-machine, which your man 

 informed us required 6 of your most pow^erful horses to work before 

 you had this steam-engine, and he said that he can now thrash 48 

 bushels more per day than ever he did with the 6 horses. During the 

 whole time I was there the safety-valve was never loaded up to 60 lbs. 

 per inch. The greatest number of revolutions was about 150 per minute, 

 and the least 120. 



I had the barn clean swept, and thrashed for 10 minutes, and had 

 5^ bushels of clean wheat measured up. This is at the rate of 330 

 bushels per day of 10 hours; during the 10 minutes I was beside the 

 engine, no steam escaped the safety-valve ; the weight on the lever was 

 just 10 inches from the fulcrum, which is equal to a pressure of nearly 60 

 lbs. per inch, and the engine made regularly 150 revolutions per minute. 



The diameter of the cylinder is 6 inches, and the length of the stroke 

 is 12^, and there was no deficiency of steam to keep the engine at work 

 all the time we were there, and your man informed me there never 

 was any stoppage for lack of steam. The length of the boiler is 8 feet, 

 its circumference outside is 9 feet 2 inches. It is constructed on the 

 Cornish principle : the fire-tube is oval, 2 feet wide and 18 inches high ; 

 this space forms the fire-place and the ash-pit. The water is heated in a 

 cistern at the end of the boiler by the heated air, which going from the 

 furnace into the smoke-flue, passes through this cistern : it is heated 

 to about 150° before it is forced into the boiler. 



