Your letter of the 7th has been duly recieved with the plate therein inclosed describing your hydraulic engine on which you are pleased to ask my opinion. it’s combinations are full of ingenuity, and especially that for converting a rectilineal into a rotatory motion without the great loss of force occasioned by the ordinary means of a crank. but long experience and multiplied disappointments have taught me to be cautious in pronouncing on the effect of a new mechanical invention, from it’s theory only. there are so many circumstances which theory does not embrace, and which still affect the execution that nothing but the actual trial of the machine itself at large can assure us of it’s effect. I confess too that in the present case I do not see the benefit derived from the interposition of the rack work between the stroke of the water, and the spur wheel intended to be the first mover of whatever machinery is applied to it: why the water should be made to give a direct motion first, to be converted afterwards by machinery into a rotatory one, rather than let the same quantity of water from the same height strike at once a bucket in the periphery of the fly wheel, and give thus the same rotatory motion, without the intervention and consequent friction of any machinery. however I must say that I have but little studied this machine. I am out of the habit of these studies, and disposed at present to lighter attentions only. but you have the machine itself in action at German town. you have in Philadelphia mathematicians and mechanics of the first order in the US. their examination and report of the effects they see must silence all the doubts & questions arising from a mere view of a paper drawing. wishing you therefore every success which your time & ingenuity may be found to have justly merited I add the assurances of my respect.

Th: Jefferson