| Description | Dear Sir
I got safe home on Wednesday Last week. When you was so kind as to express a desire to be concerned in My fire engine I was sorry I could not Imediatly make you an offer the Case is this By several Unsuccessfull projects & expensive Experiments I had Involved myself in a considerable debt before I had brought the theory of the fire engine to its present State about three years ago a Gentleman who was concerned with me dyed. as I had at that time conceived a very Clear Idea of my Present Improvements & had even made some tryal of them tho not so satisfactory as has been done since Doctor Roebuck agreed to take my debts upon him & to lay out whatever more money was necessary either for Experiments or securing the Invention for which cause I made over to him two thirds of the property of the Invention the debt, & expences are now about £1200. I have been since that time Imployed in Constructing several working fire engines on the Common Principles as well as in trying experiments to verify the theory. As the doctor from his engagements at Bon-ness & other bussiness cannot pay much attention to the executive part of this the Greatest part of it must devolve on me who am from my natural Inactivity want of health & resolution Incapable of it It gave me great Joy when you seemed to think so favourably of our scheme as to wish to engage in it I thereupon made it my bussiness as soon as I got home to wait on the doctor & propose you as one I wished he would make an offer to which he agreed to with a great deal of pleasure & will write to you in a few days that If agreeable you may be a third part Concerned on paying the half of the cost & whatever you may think the risque he has run deserves which last he leaves to yourself If you should not chuse to engage on these terms we will make you an Offer when the whole is more perfect which I hope it will soon be. the Objections against the engine before the tryals made Last winter were. that it might be difficult to make a piston sufficiently steam tight without water or some other fluid above it. Water cannot be used because if any of it got in it would boil & occasion a loss of heat. Oil of some kind was the next thought of but possibly it might be destroyed in time by the heat the next Objection was that the Vacuum Might not be formed by exhaustion sufficiently sudden or sufficiently perfect
On tryall tallow being employed to kee[p the] piston tight answered perfectly well & [did not] appear to be changed in all the [tryals] made but on removeing the tallow em[ployed] from above the piston it was found to be so tight as to Lose only 4 Strokes in . . . the want of it in Large engines this de[fect] would be Lessened in proportion as the Squares of their . . .
In answer to the second Objection the [vacuum] was formed sufficiently & very perfect that is within one sixth part . . . if this Reciprocating engine should not . . . it must be some Mechanical difficulty which I think we may certainly get the better of. If Doctor Small shoucl chuse to be concerned with you in this I have reason to think it would be agreeable to Doctor Roebuck & would be highly so to me If you should not chuse to engage with this affair in its present state or at any rate you will lett this Letter remain a secret except to Doctor Small I shall at any rate write you again soon & am Dear Sir
Your's James Watt
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