VATUOUS INVENTIONS. 13 



whole height of water; and as the stream is so very small, it 

 will not admit of losing any part of the power. 



" To erect a machine so high, to engage the whole fall, would 

 be, I fear, more expense than the power you would get would 

 warrant ; therefore I w r ould recommend it to be made use of in 

 a cylinder, in the same way as we use falls of water of 200 feet 

 in our Cornish copper mines. We allow one-third loss for 

 friction and leakage in those machines ; but your machine being 

 so very small, the loss will exceed that proportion ; therefore I 

 cannot promise you above one-half of the real weight and fall 

 to be performed on your machinery, and that must be by a 

 well-executed machine, for a small defect would destroy the 

 value of so trifling a power. 



" As there is no expansion in water, it will be somewhat diffi- 

 cult to make the machine turn the centres with a fly-wheel, for 

 if the valve shuts a little too early or too late for the turn of the 

 crank over the centre, the fly- wheel's velocity must break 

 something by confining the water between the*piston and the 

 bottom of the cylinder, which, after the valve is shut, cannot 

 make its escape, and not having an elastic principle, the piston 

 will strike as dead on the water as on a piece of iron, because, 

 unless the valve is shut by the engine before the stroke is 

 finished, it cannot shut at all. 



" I know persons who have attempted to put fly-wheels on 

 pressure-engines of this kind, but never yet has one been made 

 to work rotative. I do not see much difficulty in making an 

 engine of this kind to work a crank and fly-wheel, by connect- 

 ing an air-vessel with the cylinder to receive the pressure and 

 contract and expand and shut the valves, the same as in steam- 

 engines. 



" A machine on this plan ought to be placed as near the low 

 level as possible. If I furnish you with drawings and directions 

 for the executing of the work yourselves, I shall charge you 

 fifteen guineas for them. If I send the machine finished, the 

 chai'ge will be 50?. 



'Your objections respecting steam-engines I do not doubt 

 are correct, when executed by persons who do not understand 

 the construction of them. In England some persons privately 



