He spent the spring of 1796 in Philadelphia, where he delivered a series of lectures on the evidences of revelation to crowded audiences, including most of the members of the United States Congress, at that time sitting in Philadelphia, and of the executive officers of the Government. He delivered a second series on the same subject in the spring of the following year, but with less success, partly owing, his son imagines, to the novelty of the thing having passed away, and partly from prejudices that began to be excited against him on account of his supposed political principles. In reality Priestley took even less interest in the politics of America than he had done in those of his own country. He seldom read the debates in Congress, and beyond Adams and Jefferson he knew few of the leading politicians. He never attended a political meeting or took part directly or indirectly in an election, and excepting an article in a newspaper called “Aurora,” or “Maxims of Political Arithmetic,” and signed “A Quaker in Politics,” he wrote nothing on the subject of politics. At that period political feeling ran high and politics were the one subject of conversation, and to some extent, therefore, he could not escape their discussion, but it was noticed that he always argued on the side of liberty. As regards British politics his speculations went no further than a reform in Parliament, such as that which was accomplished less than thirty years after his death. He had no desire to see changed the constitution of the kingdom as vested in King, Lords and Commons.
“He used frequently to say,” says his son, “and it was said of him, that though he was an Unitarian in religion he was in that country a Trinitarian in politics. When he came to America he found reason to change his opinions, and he became a decided friend to the general principles and practice of a completely representative Government, founded upon universal suffrage, and excluding hereditary privileges, as it exists in this country. This change was naturally produced by observing the ease and happiness with which the people lived, and the unexampled prosperity of the country.”
But in his feelings he was still an Englishman. He never was naturalised, saying that as he had been born and had lived an Englishman he would die one, let what might be the consequence.
Towards the end of 1797 his new library and laboratory were finished, his books once more arranged and much of his old apparatus installed. He found workmen in Northumberland who could repair his instruments and make such new ones as he wanted. He was thus able to resume the kind of life he led at Birmingham, spending much of the day in the laboratory or alternately in his study, sometimes engaged on experimental philosophy, at other times in the composition of the theological works which seemed to flow in an unending stream from his pen. He delighted to walk in his garden and to view the beautiful prospect it afforded him of the river and the distant landscape. He had, too, a kindly interest in the whole community, and noted with pleasure the many little improvements going forward in and about the town. There was no apparent abatement in the vigour of his mind or in the keenness and enthusiasm with which he followed the extraordinary expansion of the science he loved so well during the opening years of the nineteenth century. In a letter to Humphry Davy, then at the outset of his brilliant career, he says:—
“It gives me peculiar satisfaction that, as I am far advanced in life and cannot expect to do much more, I shall leave so able a fellow-labourer of my own country in the great fields of experimental philosophy.... I rejoice that you are so young a man; and perceiving the ardour with which you begin your career I have no doubts of your success.”
The following letter to his old friend Mrs Barbauld, with whom he kept up a correspondence to the last, gives some account of his condition at this time:—
“Dear Madam,—This will, I hope, be delivered, as it will be conveyed by my son. How happy should I think myself to wait on you and Mr Barbauld in person. Should there be a peace, I do promise myself that pleasure, but at present this great blessing seems to be at a great distance. How many melancholy changes have taken place since I left England, and among these is the death of Dr Enfield, a man at least ten years younger than me, and to appearance more healthy. I am also much alarmed at the accounts I receive of your brother [Dr John Aiken], whom I left in perfect health, but the last were rather more favourable. His life is of great value, both to his relatives, acquaintances and the world at large, few men having been more usefully employed. I am willing to hope he is yet reserved for more usefulness.
“When I compare the perturbed state of Europe with the quiet of this place I wish all my friends were here, provided they could find sufficient employment to be happy; but if they be like myself they must be content to be idle, except so far as they can make themselves employment in their closets. My library and laboratory sufficiently occupy me, and of common society I have as much as I want. A few more rational Christians to form a society would make this place a paradise to me, and this would be wanting in many parts of England.
“It is a pleasure to be in a place that is continually and visibly improving, and this is the case here to an astonishing degree. In every year we find a very sensible difference, and in all probability improvements of all kind will go on more rapidly than ever. Nature has done everything that can be done for any place. Perhaps you have seen the views of it taken by Miss Daich. They are not by any means too flattering.
“Could I have my daughter here I should be happy indeed. But this, I fear, is not likely to be accomplished, owing to the strange obstinacy and prejudice of Mr Finch. Her trials must be very great, but she is naturally cheerful, and has a strong sense of religion, which, I hope, will support her. This, sufficiently impressed, will make us equal to everything. Your kindness to her affects me much. A friend in need is a friend indeed. Something will, I hope, be done for her before my son returns, but what it can be I do not know. Her uncle has some proposal to make to my son in her favour, but the obstinacy of Mr Finch may defeat everything.
“You have obliged me very much by the exquisite little poem you sent me. I hope you will add to the obligation by the communication of the fragment on the ‘Game of Chess,’ or any other little piece you may think proper to send me. You had no copy of your first poem to my wife, or I should value that above any other, and also the little poem you wrote on the birth of Joseph.
“I shall always be very happy to hear from you; and, with my best respects to Mr Barbauld, I am, dear Madam, yours sincerely, J. Priestley.
“Northumberland, Dec. 23, 1798.
“Mrs Barbauld, Hampstead,
near London.”
His son has given us a faithful picture of his closing years and of the serenity of the evening of his life.
“For the last four years of his life he lived under an administration, the principles and practice of which he perfectly approved, and with Mr Jefferson, the head of that administration, he frequently corresponded, and they had for each other a mutual regard and esteem. He enjoyed the esteem of the wisest and best men in the country, particularly at Philadelphia, where his religion and his politics did not prevent his being kindly and cheerfully received by great numbers of opposite opinions in both, who thus paid homage to his knowledge and virtue.”
In 1800 he put together his last scientific work, and the one which he regarded as the crown of all his efforts, viz., his Doctrine of Phlogiston Established. It can never be said of Priestley that he was to one thing constant never: versatile as he was, and with an extraordinary capacity for adaptation and change in matters of philosophy and theological doctrine, he was ever constant to phlogiston.