The bargainings with mine-owners brought on intense heartaches and broke Watt down completely. Boulton had to go to him again in Cornwall in the autumn of 1779, and as usual succeeded in adjusting many disputes by wise compromises with the grasping owners which Watt's strict sense of justice had denied. Many of these had paid no royalties for years, others disputed Watt's unerring register of fuel consumption (another of his most ingenious inventions now in general use for many purposes), a more heinous offense in his eyes than that of non-payment. "The rascality of man," he writes, "is almost beyond belief." He never was more despondent or more irritable than now. No one was better aware of his weakness than himself. In short, his heartaches and nervousness unfitted him for business. As usual, he attributed his discouragement chiefly to his financial obligations. The firm was as hard pressed as ever. Indeed a new source of danger had developed. Fothergill's affairs became involved, and had it not been for Boulton's capital and credit, the firm of Boulton and Fothergill could not have maintained payment. This had caused a drain upon their resources. Boulton sold the estate which had come to him by his wife, and the greater part of his father's property, and mortgaged the remainder. It is evident that the great captain had taken in hand far too many enterprises. Probably he had not heard the new doctrine: "Put all your eggs in one basket and then watch that basket." He had even ventured considerable sums in blockade running during the American Revolutionary War. It was not without good reason, therefore, that the more cautious Scot addressed to him so many pathetic letters: "I beg of you to attend to these money matters. I cannot rest in my bed until they have some determinate form." Watt's inexperience in money matters caused apprehensions of ruin to arise whenever financial measures were discussed. He was at this time utterly wretched, and Mrs. Watt at last became anxious, long and bravely as she had hitherto borne up and striven to dispel her husband's fears. Never before had she ventured to speak to Boulton upon the subject. She now broke the silence and wrote him in Cornwall a touching letter, stating that her husband's health and spirits had become much worse since Boulton had left Soho. "I know there are several things that so prey upon his mind as to render him perfectly miserable. They never cross his mind, but he is rendered unfit to do anything for a long time." She describes these financial demons that torment him and begs that her writing should not be told to Watt, as it might only add to his troubles. The appeal brings Mrs. Watt before us in a most engaging light.