Letter from W. Hann, Killingworth to John Wesley Hackworth

Killingworth
29th Sept. 1844

Dear Sir,
I duly receive your letter of the 20th inst. and quite agree in your opinion, that two motions are necessary in the case of the motion first sketched, being used by itself or not attached to wheels – as instead of two, there are four dead points. In my letter I stated that I could not satisfy myself that the apparatus sketched would answer alone (and threw it out for your improvements upon it) nor do I yet see how it could be made a good motion – in the first place – the connecting rod being of the same length as the crank (1/4th of the stroke) there would be four dead points, or the piston rod would be four times in the line of the centres, in the course of the entire stroke: instead of twice only, as in the common engines, and two of these, at that part of the stroke when the engine has the full force of the steam, which would be bad in both theory and practice. 2nd the motion whether with one or two engines would be extremely variable; thus at 10 degrees it would be *0*, at 45 degrees = 1*, at 90 degrees = *0, at 135 degrees = 1*, and at 180 degrees = *0 again, - 3rd The reflected or obligne [sic] force would be greater than that of any other method I know, and would require extremely strong guide bars etc. If has however one advantage, that is, a short connecting rod, but the disadvantages more than counterbalance this.
I have spoken this far of it separately – but when in connection with the wheels, as you first proposed, I don’t see where it is “decidedly objectionable”, and if you can find leisure to write, would be happy to know your objections to it. The wheels you will observe receive the reflected or resultant force which they give out at the periphery or teeth, thus preventing that kind of friction, and effecting a parallel acting force; and greater uniformity of motion, which is not new, is a valuable improvement. There can be no doubt, but that other methods of attaching two piston rods to the wheels, besides the one pointed out by you might be adopted, but I think there is the least expenditure of material about it, and that it occupies less space than any other I can devise. If you would turn the subject over in your mind, and if any better arrangement presents itself, you will perhaps be so good as sketch it, and I will give my thoughts upon it, before you proceed to make the intended model or pattern engine.
I trust your father is now in his usual good health and remain
Dear Sir, Yours Respectfully
W.Hann
Mr J W Hackworth
P.S You will see, in the Durham Advertiser, that the Lending of Westerton Coals, Smithwork etc etc is to let – Tenders 8th Oct.