McGrigor was Watt's second father-in-law.

He wishes to revise 'my survey of the ground between Inverness and Fort William' but fears 'the estimate is less than it can be done for'. Re Mr. Arkwright 'he is, to say no worse, one of the most self sufficient ignorant men I have ever met with', yet 'certainly a man of merit in his way, and one to whom Britain is much indebted and whom she should honour & reward'. Watt gives details of past dealings with Arkwright, adding that 'our rotative engines ... are certainly very applicable to the driving of cotton mills'. He continues 'As Mr Boulton is absent I cannot give any answer .. about the Engineership of this Great Canal'. His mind is 'almost wholly turned toward the steam engine', and 'business which is now very extensive takes up all the time that bad health will permit me to work'. He says 'we must ... go to law with some people who encroach on our patent rights'. He adds his views on taxation 'which is exclusively leveled at trade and manufactures'. And 'our business is going on successfully, and could we only depend on its durability we need look for no better'.