Though he has been considered as fond of controversy, and that his chief delight consisted in it, yet it was far from being true. He was more frequently the defendant than the assailant. His controversies, as far as it depended upon himself, were carried on with temper and decency. He was never malicious, nor even sarcastic or indignant, unless provoked.
Priestley was a very busy man and a very industrious man, but he had not the power of sustained and concentrated application to a single subject which is the characteristic of men of great intellectual eminence. In this respect he was far inferior to his contemporaries Watt and Cavendish. His quick and active mind enabled him rapidly to assimilate the ideas of others, but it may be doubted, even in theology, whether he pushed his convictions and doctrinal beliefs beyond the limits reached by previous thinkers. His philosophy, as Huxley has pointed out, contains little that will be new to the readers of Hobbes, Spinoza, Collins, Hume and Hartley. “It does not appear,” says his son, “that he spent more than six or eight hours per day in business that required much mental exertion.” In his diary he laid down the following daily arrangements of time for a minister’s studies:—Studying the Scriptures, one hour. Practical writers, half-an-hour. Philosophy and History, two hours. Classics, half-an-hour. Composition, one hour—in all five hours. “All which,” he adds, “may be conveniently dispatched before dinner, which leaves the afternoon for visiting and company, and the evening for exceeding in any article if there be occasion.”
His son tells us that for many years of his life he never spent less than two or three hours a day in games of amusement, as cards and backgammon, but particularly chess, at which he and his wife played regularly three games after dinner and as many after supper. As his children grew up, chess was laid aside for whist or some round game at cards, which he enjoyed as much as any of the company. He was fond, too, of bodily exercise, and was particularly attached to his garden, in which he worked constantly. His laboratory also afforded him exercise, as he never employed an assistant, and never allowed anyone even to light his fire.
The attention, he says, which he paid to the phenomena of his own mind, made him sensible of some great defects in its constitution. He was, he says, from an early period, subject to a “most humbling failure of recollection,” so that he sometimes lost all ideas of both persons and things that he had been conversant with. He says, “I have so completely forgotten what I have myself published, that in reading my own writings what I find in them often appears perfectly new to me, and I have more than once made experiments the results of which had been published by me.”
Apprised of this defect he never failed to note down as soon as possible everything that he wished not to forget. The same failing led him to devise and have recourse to a variety of mechanical expedients to secure and arrange his thoughts, which were of the greatest use to him in the composition of large and complex works, and what he says excited the wonder of some of his readers would only have made them smile had they seen him at work. “But by simple and mechanical methods one man shall do that in a month which shall cost another, of equal ability, whole years to execute. This methodical arrangement of a large work is greatly facilitated by mechanical methods, and nothing contributes more to the perspicuity of a large work than a good arrangement of its parts.”
What he learned to know with respect to himself tended much, he says, to lessen both his admiration and his contempt of others.
“Could we have entered into the mind of Sir Isaac Newton, and have traced all the steps by which he produced his great works, we might see nothing very extraordinary in the process. And great powers with respect to some things are generally attended with great defects in others; and these may not appear in a man’s writings. For this reason, it seldom happens but that our admiration of philosophers and writers is lessened by a personal knowledge of them.”
Great defects may, however, be more than counter-balanced by great excellences, and accordingly he hopes that his defect of recollection, possibly due to a want of sufficient coherence in the association of ideas formerly impressed, might arise from a mental constitution more favourable to new associations, so that what he lost with respect to memory may have been compensated by what is called invention, or new and original combinations of ideas.
In the domestic relations of life he was uniformly kind and affectionate. As was truly said of him on Darton’s portrait, “Not malice itself could ever fix a stain on his private conduct or impeach his integrity.”