That Priestley greatly enjoyed and profited by his Christmas in London is evident from the terms in which he refers to it in a letter to Canton under date February 14, 1766.
“The time I had the happiness to spend in your company appears upon revision like a pleasing dream. I frequently enjoy it once again in recollection, and ardently wish for a repetition of it. I wish, but in vain, that it may ever be in my power to return in kind your generous communication of philosophical intelligence and discoveries.”
He concludes the letter by expressing a desire to become a Fellow of the Royal Society.
Benjamin Franklin, journeyman printer and journalist, statesman and diplomatist, was about sixty years old when Priestley, then a man of little more than half his age, first made his personal acquaintance. The Royal Society, which had formerly ridiculed the discoveries which have given Franklin his undisputed position as one of the most eminent natural philosophers of his time, had paid him, although still a British subject, the distinguished compliment of making him an honorary fellow. At the time of Priestley’s coming to town he was occupied with the great struggle on behalf of the American Colony which ended in the defeat of the Stamp Act, and his famous examination before a Committee of Parliament had made him an object of great popular interest. During the eight or nine succeeding years in which Franklin remained in England his acquaintance with Priestley grew into the closest friendship, and there can be no question that the friendship reacted powerfully on Priestley’s work as a political thinker and as a natural philosopher. Indeed, it may be truthfully said that Franklin made Priestley into a man of science.
As the result of this intercourse with Canton and Franklin, Priestley offered to compile what he called “a distinct and methodical account” of the history of discoveries in electricity, provided he could be supplied with the necessary books. Franklin warmly seconded the proposal, and undertook, with the assistance of friends, to furnish all existing literature on the subject. As a matter of fact almost the whole of the historical account in Priestley’s book is taken from the Philosophical Transactions of the Royal Society, which was then the chief source of information concerning electrical science, inasmuch as the English electricians of that period, in addition to their own original papers, which were both numerous and important, introduced into the Transactions detailed accounts of all the principal books on electricity published abroad. In putting together his work, Priestley, having, as he says, a pretty good machine, was led to endeavour to ascertain several facts which were in dispute, and was thus led by degrees into a large field of experimental inquiry, in which he spared no expense that he could possibly afford. One of the most important of his discoveries is that charcoal is a good conductor. He describes coloured circles produced by receiving discharges from 21 square feet of glass on metal plates. When an electrical battery is discharged light bodies placed near the electric circuit are moved. Priestley ascribes this motion to what he calls the force of the lateral explosion, and he conceives it to depend upon the sudden elasticity given to the air. He found that a long circuit conducts much worse than a short circuit, even when the conductors are the same; also, that when the circuit contains an imperfect conductor a spark passes to bodies near, no electricity being communicated.
The work necessitated much correspondence with Franklin and others of his philosophical friends in London, and much of his leisure was devoted to his own experimental observations. Nevertheless, the book was completed in less than a year. Hasty and imperfect as it was, “The History and Present State of Electricity. With Original Experiments, illustrated with Copperplates,” was well received and ran through five editions in its author’s lifetime. Its publication at once stamped Priestley as a man of science; it secured him recognition as such in scientific circles at home and abroad, and was the immediate cause of his election, on June 12, 1766, into the Royal Society. The growing interest in the subject induced him to put together a Familiar Introduction to the Study of Electricity, which had also a considerable measure of success and was the means of popularising a knowledge of the main facts then known concerning Frictional Electricity. Priestley was instrumental in reviving the use of large electrical machines and batteries. The first of the large machines for which Nairne became famous was constructed in consequence of a request made to Priestley by the Grand Duke of Tuscany to procure for him the best machine that could be made in England. One of his machines, which figured in his History, and also in his Familiar Introduction, is in the possession of the Royal Society.
CHAPTER V
Goes to Leeds as minister of the Mill Hill Chapel—Resumes his studies in Speculative Theology—The Theological Repository—Becomes a Unitarian—Priestley as a controversialist—His Theory and Practice of Perspective—His literary characteristics—Begins his inquiries on Pneumatic Chemistry—His invention of soda-water—Receives the Copley Medal of the Royal Society.
Although Priestley lived in philosophic contentment with his lot at Warrington, happy in his occupations and in the society of congenial colleagues, the circumstances of the Academy were not fortunate. The institution never wholly recovered from the unhappy differences between the trustees and the first head of the Educational Staff, and in time many of the subscribers grew lukewarm in their support. Priestley had a remarkable power of adapting himself to his environment; he was one of the most even-tempered of men and had a capacity for being cheerful that would have extorted admiration even from Socrates. “But,” says Miss Aiken, “the Alma Mater of Warrington was ever a niggardly recompense of the distinguished abilities and virtues which were enlisted in her service.” One hundred pounds a year, with a house and a few boarders—hungry lads at £15 a year, exclusive of washing and candles—meant little towards the res angusta domi. Moreover, little Sarah Priestley had made her appearance, and the uncertain prospects which were before that young lady, coupled with the condition of her mother’s health, which was not wholly satisfactory at Warrington, led him to contemplate the expediency of giving up school-mastering and of resuming his profession of the ministry. Accordingly he was induced to accept an invitation to take charge of the congregation of Mill Hill Chapel, at Leeds, where he was already pretty well known, and thither he removed in 1767.[12]
Although it was no part of his duty to preach when at Warrington, he had from choice continued the practice, and wishing to maintain the character of a Dissenting minister, he had, as we have already seen, been ordained whilst there. His tendency to stammer was still a difficulty. Indeed, whilst at Nantwich it was so marked that he had almost resolved to abandon the calling. By reading aloud and very slowly every day, and by taking pains, he in some measure got the better of his defect, but he never wholly overcame it.