In the correspondence between the partners on these various topics, we seem to see the ideas out of which so many inventions grew, in their various stages of birth, growth and development. They concealed nothing from each other, but wrote with the most perfect unreserve. Each improved on the other’s ideas,--Watt upon Boulton’s, and Boulton upon Watt’s; both experimenting on the same subject at the same time, and communicating the results in the most elaborate detail. The phrase often occurs in their letters: “I write thus fully _that you may see exactly what is passing in my mind_.” The letters were sometimes of extraordinary length, one of Boulton’s (dated 25th September, 1781) extending to eight pages folio, closely written, containing upwards of 4000 words. Scarcely a day passed without their spending several hours in writing to each other. Boulton also kept up a correspondence with Mrs. Watt, in addition to his elaborate letters to her husband. The lady entered into various matters of personal interest, describing her occupations and domestic pursuits, and communicating the state of her husband’s health, which was a matter of no less interest to Boulton than to herself. As the autumn set in with its fogs and rains, Watt’s headaches returned with increased severity, and he repeatedly complained to Boulton of being “stupid and ill, and scarcely able to think.” “I tremble,” said he, “at the thought of making a complete set of drawings. I wish you could find me out a draughtsman of abilities; as I cannot stand it much longer.”[229] Watt’s temper was also affected by the state of his health; and he confessed that he felt himself not at all cut out for the work he had to do, so far as related to business: “I am not philosopher enough,” he said, “to despise the ills of life; and when I suffer myself to get into a passion, I observe it hurts me more than it does anybody else. I never was cut out for business, and wish nothing so much as not to be obliged to do any; which perhaps will never fall to my lot; therefore I must drag on a miserable existence the best way I can.”[230] [229] Watt to Boulton, 20th September, 1781. [230] Watt to Boulton, 18th October, 1781.