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CHAPTER XVIII. FRIENDS OF BOULTON AND WATT - THE LUNAR SOCIETY.
As men are known by the friends they make and the books they read, as well as by the recreations and pursuits of their leisure hours, it will help us to an appreciation of the characters of Boulton and Watt if we glance briefly at the social life of Soho during the period we have thus rapidly passed under review. Boulton was of a thoroughly social disposition, and made friends wherever he went. He was a favourite alike with children and philosophers, with princely visitors at Soho, and with quiet Quakers in Cornwall. When at home, he took pleasure in gathering about him persons of kindred tastes and pursuits, in order at the same time to enjoy their friendship, and to cultivate his nature by intercourse with minds of the highest culture. Hence the friendships which he early formed for Benjamin Franklin, Dr. Small, Dr. Darwin, Josiah Wedgwood, Thomas Day, Lovell Edgeworth, and others equally eminent out of which eventually grew the famous Lunar Society.
Towards the close of last century, there were many little clubs or coteries of scientific and literary men established in the provinces, the like of which do not now exist, — probably because the communication with the metropolis is so much easier, and because London more than ever absorbs the active intelligence of England, especially in the higher departments of science, art, and literature. The provincial coteries of which we speak, were usually centres of the best and most intelligent society of their neighbourhoods, and were for the most part distinguished by an active and liberal spirit of inquiry. Leading minds attracted others of like tastes and pursuits, and social circles were formed which proved in many instances the source of great intellectual activity as well as enjoyment. At Liverpool, Roscoe and Currie were the centres of one such group; at Warrington, Aikin, Enfield, and Priestley, of another at Bristol, Dr. Beddoes and Humphry Davy of a third; and at Norwich, the Taylors and Martineaus of a fourth. But perhaps the most distinguished of these provincial societies was that at Birmingham, of which Boulton and Watt were among the most prominent members.
From an early period, the idea of a society, meeting by turns at each other's houses, seems to have been entertained by Boulton. It was probably suggested in the first place by his friend Dr. Small. The object of the proposed Society was to be at the same time friendly and scientific. The members were to exchange views with each other on topics relating to literature, art, and science; each contributing his quota of entertainment and instruction. The meetings were appointed to be held monthly at the full of the moon, to enable distant members to drive home by moonlight and this was the more necessary as some of them — such as Darwin and Wedgwood — lived at a considerable distance from Birmingham.
When Watt visited Soho in 1768, on his way home from London to Glasgow, some of the members of the Society - Dr. Small, Dr. Darwin, and Mr. Keir were invited to meet him at ‘l'hotel de l’amitia Sur Handsworth Heath’, as Boulton styled his hospitable mansion. The Society must, however, have been in a somewhat undefined state at even a considerably later period, as we find Boulton writing to Watt in 1776, after the latter had settled in Birmingham, "Pray remember that the celebration of the third full moon will be on Saturday, March 3rd. Darwin and Keir will both be at Soho. I then propose to submit many motions to the members respecting new laws and regulations, such as will tend to prevent the decline of a Society which I hope will be lasting." The principal members, besides those above named, were Thomas Day, R. Lovell Edgeworth, Samuel Calton, Dr. Withering, Baskerville the printer, Dr. Priestley, and James Watt. Each member was at liberty to bring a friend with him, and thus many visitors of distinction were present at the meetings of the Society, amongst whom may be named Mr. Smeaton, Dr. Parr, Sir Joseph Banks, Sir William Herschel, Dr. Solander, De Luc, Dr. Camper, and occasional scientific foreigners.
Dr. Darwin was regarded as the patriarch of the Society. His fame as a doctor, philosopher, and poet, was great throughout the Midland Counties. He was extremely speculative in all directions, even in such matters as driving wheel-carriages by steam, — also a favourite subject of speculation with Mr. Edgeworth.  Dr. Darwin's time, however, was so much engrossed by his practice at Lichfield, that he was not very regular in his attendance at the meetings, but would excuse himself for his absence by such a letter as the following:—
"DEAR BOULTON,- I am sorry the infernal divinities who visit mankind with diseases, and are therefore at perpetual war with Doctors, should have prevented my seeing all your great men at Soho to-day. Lord! what inventions, what wit, what rhetoric, metaphysical, mechanical, and pyrotechnical, will be on the wing, bandied like a shuttlecock from one to another of your troop of philosophers! while poor I, I by myself I, imprisoned in a postchaise, am joggled, and jostled, and bumped, and bruised along the King's high-road, to make war upon a stomach-ache or a fever!" 
While Dr. Darwin and Mr. Edgeworth were amongst the oldest members of the society, Dr. Priestley, the discoverer of oxygen and other gases, was one of the most recent. We find Boulton corresponding with him in 1775,  principally on chemical subjects, and supplying him with parcels of fluor spar for purposes of experiment. Five years later, in 1780, he was appointed minister of the Presbyterian Congregation assembling in the New Meeting-house, Birmingham; and from that time forward he was one of the mom active members of the Lunar Society, by whom he was regarded as a great acquisition.
Priestley was a man of extraordinary gifts and accomplishments. He had mastered many languages before he was twenty years old. He was well versed in mechanical philosophy and metaphysics, a skilled dialectician, and the most expert chemist of his time. Possessed by an irrepressible activity and untiring perseverance, he became an enthusiast on whatever subject he undertook, whether it was an inquiry into history, theology, or science. He himself likened experimental philosophy to hunting, and in his case it was the pursuit of facts that mainly concerned him. He was cheerful, hopeful, and buoyant; possessed of a most juvenile temperament; happiest when fullest of work; ranging from subject to subject with extraordinary versatility; laying aside metaphysics to pursue experiments in electricity, next taking up history and politics, and resting from these to experiment on gases, — all the while carrying on some public controversy on a disputed point in religion or politics. For it is a curious fact, that gentle, affectionate, and amiable though Priestley was, devout in temperament, and single-minded in the pursuit of truth,  he was almost constantly involved in paper wars. He described himself, and truly, as "one of the happiest of men;" yet wherever he went, in England or America, he stirred up controversy and exasperated opponents, seeming to be the very Ishmael of polemics.
At the time when he settled at Birmingham, Priestley was actively engaged in prosecuting inquiries into the constitution of bodies. He had been occupied for several years before in making investigations as to the gases. The discovery of carbonic acid gas by Dr. Black of Edinburgh, had attracted his attention; and, living conveniently near to a brewery at Leeds, where he then was, he proceeded to make experiments on the fixed air or carbonic acid gas evolved during fermentation. From these he went on to other experiments, making use of the rudest apparatus, - Phials, tobacco-pipes, kitchen utensils, a few glass tubes, and an old gun-barrel. The pursuit was a source of constant pleasure to him. He had entered upon an almost unexplored field of science. Then was the childhood of chemistry, and he gazed with large-eyed wonder at the marvels which his investigations brought to light. He had no teacher to guide him — nothing but experiment; and he experimented constantly, carefully noting the results. Observation of facts was his great object; the interpretation of the facts he left to others. Such was Priestley, and such were his pursuits, when he settled at Birmingham in 1780.
There can be little doubt that his enthusiasm as an experimenter in chemistry exercised a powerful influence on the minds of both Boulton and Watt, who, though both full of work, anxiety, and financial troubles, were nevertheless found taking an active interest from this time forward in the progress of chemical science. Chemistry became the chief subject of discussion at the meetings of the Lunar Society, and chemical experiments the principal recreation of their leisure hours.
"I dined yesterday at the Lunar Society (Keir's house)," wrote Boulton to Watt; "there was Blair, Priestley, Withering, Gallon, and an American 'rebel,' Mr. Collins. Nothing new except that some of my white Spathos Iron ore was found to contain more air than any ore Priestley had ever tried, and, what is singular, it contains no common air, but is part fixable and part inflammable." 
To Henderson, in Cornwall, Boulton wrote, two months later,—
"Chemistry has for some time been my hobby-horse, but I am prevented from riding it by cursed business, except now and then of a Sunday. However, I have made great progress since I saw you, and am almost an adept in metallurgical moist chemistry. I have got all that part of Bergmann's last volume translated, and have learnt from it many new facts. I have annihilated Wm. Murdock's bedchamber, having taken away the floor, and made the chicken kitchen into one high room covered over with shelves, and these I have filled with chemical apparatus. I have likewise set up a Priestleyan water-tub, and likewise a mercurial tub for experiments on gases, vapours, &c., and next year I shall annex to these a laboratory with furnaces of all sorts, and all other utensils for dry chemistry." 
The "Priestleyan water-tub" and "mercurial tub," here alluded to, were invented by Priestley in the course of his investigations, for the purpose of collecting and handling gases and the pneumatic trough, with glass retorts and receivers, shortly became part of the furniture of every chemical laboratory.
Josiah Wedgwood was another member of the Lunar Society who was infected by Dr. Priestley's enthusiasm for chemistry; and, knowing that the Doctor's income from his congregation was small, he and Boulton took private counsel together as to the best means of providing him with funds so as to place him in a position of comparative ease, and enable him freely to pursue his investigations. The correspondence which took place on the subject is creditable to all parties concerned; and the more so to Boulton, as he was embarrassed at the time by financial difficulties of the most distressing kind, as has been already explained in a preceding chapter. Wedgwood had undertaken to sound Dr. Priestley, and he thus communicated the result to Boulton:-
The Doctor says he never did intend or think of making any pecuniary advantage from any of his experiments, but gave them to the public with their results, just as they happened, and so he should continue to do, without ever attempting to make any private emolument from them to himself.
I mentioned this business to our good friend, Dr. Darwin, who agrees with us in sentiment, that it would be a pity that Dr. Priestley should have any cares or cramps to interrupt him in the fine vein of experiments he is in the midst of, and is willing to devote his time to the pursuit of, for the public good. The Doctor will subscribe, and has thought of some friends who, he is persuaded, will gladly do the same. . .
You will see by the enclosed list that one cannot decently exceed ten guineas unless it be under the cover of a friend's name, which method I shall take if I think it necessary to write more than ten; but that is the subscription I shall begin with, and for three years certain.
Dr. Darwin will be very cautious who he mentions this affair to, for reasons of delicacy which will have equal weight with us all. I mentioned your generous intention to Dr. P., and that we thought of £20 each; but that, you will perceive, cannot be, and the Doctor says much less will suffice, as he can go on very well with £100 per annum." 
Boulton wrote Wedgwood in reply, requesting that the money subscribed should be collected and paid to Dr. Priestley in such a way as not to wound his sensitive feelings. He suggested that in order to avoid this it might be better if, instead of an annual subscription, a dozen gentlemen were found to give a hundred pounds each for the purpose of buying an annuity, or investing the amount in stock for the Doctor's benefit.
"I have never yet spoken to him on the subject," he added; "I wish to avoid it, and so doth my neighbour Galton. Therefore I beg you will manage the affair so that we may contribute our mites to so laudable a plan, without the Doctor knowing anything of the matter, and favour us with a line on the subject at your leisure." 
In a subsequent part of the same letter he indicated the subject of Priestley's experiments at the time:-
"We have long talked," said he, "of Phlogiston without knowing what we talked about; but now that Dr. Priestley hath brought the matter to light, we can pour that element out of one vessel into another, can take it out of one metal and put it into another, can tell how much of it, by accurate measurement, is necessary to reduce a calx to a metal, which is easily done, and without putting that calx into contact with any visible thing. In short, this goddess of levity can be measured and weighed like other matter. For the rest, I refer you to the Doctor himself."
The discussions at the Lunar Society were not, however, exclusively chemical, but were varied according to the visitors who from time to time honoured the members with their presence. Thus, in the autumn of 1782, the venerable Smeaton, having occasion to be in Birmingham upon canal business, was invited to attend a meeting of the Society held in Watt's house at Harper's Hill. Watt thus described the evening's proceedings in a letter to Boulton, then in London:—
"He [Smeaton] grows old, and is rather more talkative than he was, but retains in perfection his perspicuity of expression and good sense. He came to the Philosophers' Meeting at my house on Monday, and we were receiving an account of his experiments on rotatives and some new ones he has made, when unluckily his facts did not agree with Dr. Moyes the blind philosopher's theories, which made Moyes contradict Smeaton, and brought on a dispute which lost us the information we hoped for, and took away all the pleasure of the meeting, as it lasted two hours without coming half an inch nearer to the point." 
A few days later, we find De Luc paying his first visit to Watt at Birmingham, accompanied by Baron Reden, who desired to inspect the Soho works. "De Luc," wrote Watt, "is a modest ingenious man. On Wednesday, Wilkinson, Reden, and he sent for me to ‘The Castle’ after dinner, and kept me to supper. On the following day De Luc came to breakfast, and spent the whole forenoon, insensing  himself with steam and steam-engines. He is making a book, and will mention us in it. Dr. Priestley came also to dinner, and we were all good company till six o'clock, when Wilkinson set off for Broseley, and they for London."
Meanwhile Priestley continued to pursue his investigations with indefatigable zeal, discovering one gas after another,  and immediately proclaiming the facts which he brought to light, so that other minds might be employed on them besides his own. He kept nothing secret. Perhaps, indeed, he was too hasty in publishing the results of experiments still unfinished, as it occasionally led him into contradictions which a more cautious method of procedure would have enabled him to avoid. But he was thoroughly honest, ingenuous, and single-minded in all his proceedings, entertaining the conviction that in the end truth would vindicate itself, and that all that was necessary was to inquire ardently, to experiment incessantly, and to publish freely.
One of the most interesting speculations to which Priestley's experiments gave rise was the composition of water. The merit of discovering the true theory has been variously attributed to Watt, to Cavendish, and to Lavoisier; and perhaps no scientific question has been the subject of more protracted controversy. It had been known for some years that a certain mixture of inflammable and dephlogisticated air (hydrogen and oxygen), or common air and hydrogen, could be fired by the electric spark. The experiment had been made by Volta and Macquer in 1776-7 and in the spring of 1781 Priestley made what he called a "random experiment" of the same kind, to entertain some philosophical friends. He exploded a mixture of common air and hydrogen in a glass globe by sending an electric spark through it, and when the explosion had taken place it was observed that the sides of the glass were bedewed with moisture. Mr. Warltire, a lecturer on Natural Philosophy at Birmingham,  was present at the experiment, and afterwards repeated it in a copper flask for the purpose of trying "whether heat is heavy or not." In the mean time, Mr. Cavendish, who had for some years been occupied in the special study of pneumatic chemistry, and satisfactorily solved the question of the true composition of atmospheric air, having had his attention directed to Mr. Warltire's experiment, repeated it in London, in the summer of 1781, employing a glass vessel instead of a copper one; and again the deposit of dew was observed on the sides of the glass. This phenomenon, which Priestley had disregarded, appeared to him to be of considerable importance, and likely to throw great light "upon the subject of the disappearance of oxygen during combustion, which he bad been pursuing experimentally by means of his well-known eudiometer." The liquid which resulted from the detonations was very carefully analysed, and proved in all the experiments with hydrogen and air, and in some of those with hydrogen and oxygen, to be pure water but in certain of the latter it contained a sensible quantity of nitric acid. Till the source of this was ascertained, it would have been premature to conclude that hydrogen and oxygen could be turned into pure water."  These experiments, however, were not published, being still regarded as inconclusive. But with the communicativeness which distinguishes the true man of science, Cavendish made them known to Priestley, and, through his friend Dr. Blagden, to Lavoisier. It was not until January, 1784, that he communicated the results of his long series of experiments on the subject to the Royal Society.
In the mean time Watt's attention had been directed to the same subject by the experiments of Priestley, and he was led to the same conclusions as Cavendish, though altogether independent of him, and by means of a different class of experiments. We find him writing to Boulton, then at Cosgarne, as follows, in 1782:—
"You may remember that I have often said that if water could be heated red hot, or something more, it would probably be converted into some kind of air, because steam would in that case have lost all its latent heat, and that it would have been turned wholly into sensible heat, and probably a total change of the nature of the fluid would ensue. Dr. Priestley has proved this by experiment. He took lime and chased out all the fixed air, and made it exceedingly caustic by long-continued and violent heat. He then added to it two ounces of water, and as expeditiously as possible subjected it again to a strong heat, and he obtained two ounces' weight of air; and, what is most surprising, a balloon which he interposed between the retort and receiver was not sensibly moistened, nor at all heated that could be observed. The air produced was but very little more than common air, and contained scarce any fixed air. So here is a plain account of where the atmospheric air comes from. The Doctor does me justice as to the theory." 
The results of this experiment were by no means conclusive. That water was composed, at least in part, of air or gas of some kind was obvious but what the gas was, and whether it existed in combination with other gases, was still a matter of conjecture. But Priestley, having proceeded to repeat Cavendish's experiment  of exploding a mixture of oxygen and hydrogen in a glass vessel, which was followed by the usual deposit of water, communicated the fact to Watt, and this at once put him on the track of the true theory. In a letter to Dr. Black, he communicated the result of Dr. Priestley's experiments, stating that "when quite dry pure inflammable air (hydrogen) and quite dry pure dephlogisticated air (oxygen) are fired by the electric spark in a close vessel, he finds, after the vessel is cold, a quantity of water adhering to the vessel equal, or very nearly equal, to the weight of the whole air. . . . Are we not then authorised to conclude, that water is composed of dephlogisticated and inflammable air or phlogiston deprived of part of their latent heat and that dephlogisticated or pure air is composed of water deprived of its phlogiston and united to heat and light; and if light be only a modification of heat, or a component part of phlogiston, then pure air consists of water deprived of its phlogiston or latent heat?  At the same time Watt wrote to Priestley, - who did not himself see the force of the experiments as establishing the true composition of water, — demonstrating the conclusions which they warranted, and which were identical with those already drawn by Cavendish.
Whether Priestley had communicated to Watt the theory of Cavendish does not appear; but it is probable that both arrived at the same conclusions independently of each other; Cavendish from the result of his own experiments, and Watt from those of Priestley. Each was quite competent to have made the discovery nor is it necessary for the fame of either to strip a leaf of laurel from the brow of the other. Moreover, we are as unwilling to believe that Cavendish would have knowingly appropriated to himself the idea of Watt, as that Watt would have knowingly appropriated the idea of Cavendish. As it was, however, Cavendish and Watt both claimed priority in the discovery; the advocates of Watt's claim resting their case mainly on the fact of his having first stated his views on the subject in writing, in a letter which he wrote to Dr. Priestley for the purpose of being read to the Royal Society in April, 1783. Before that letter was read, Watt asked that it should be withheld until the results of some new experiments of Dr. Priestley could be ascertained. These proving delusive, Watt sent a revised edition of the letter to his friend De Luc, in November, but the reading of it was delayed until the 29th April, 1784, before which time on the 15th January, Cavendish's paper on the same subject had been communicated to the Society. Watt was much annoyed at the circumstance, and alleged that Cavendish had been guilty of "plagiarism."  At a late period of his life, when all bitter feelings on the subject had subsided, Watt declared himself indifferent to the subject of controversy: "After all," said he, "it matters little whether Cavendish or I discovered the composition of water; the great thing is, that it is discovered."
Pneumatic chemistry continued to form the principal subject of discussion at the Lunar Society, as we find from numerous references in Boulton and Watt's letters. "The Lunar Society," wrote Watt to his partner, "was held yesterday at Mr. Galton's at Barr. It was rather dull, there having been no philosophical news lately except Mr. Kirwan's discovery of an air from phosphorus, which takes fire of itself on being mixed with common or dephlogisticated air."  Among Watt's numerous scientific correspondents was M. Berthollet, the eminent French chemist, who communicated to him the process he had discovered of bleaching by chlorine. Watt proceeded to test the value of the discovery by experiment, after which he recommended his father-in-law, Mr. Macgregor, of Glasgow, to make trial of it on a larger scale. This, however, was postponed until Watt himself could find time to superintend it in person. At the end of 1787, we find him on a visit to Glasgow for the purpose, and writing Boulton that he is making ready for the trial. "I mean," he writes, "to try it to-morrow, though I am somewhat afraid to attack so fierce and strong a beast. There is almost no bearing the fumes of it. After all, it does not appear that it will prove a cheap way of bleaching, and it weakens the goods more than could be wished, whatever good it may do in the way of expedition."  The experiment succeeded, and we find Mr. Macgregor, in the following February, "engaged in whitening 1,500 yards of linen by the process." The discovery, not being protected by a patent, was immediately made use of by other firms; but the offensive odour of the chlorine was found exceedingly objectionable, until it was discovered that chlorine could be absorbed by slaked lime, the solution of which possessed great bleaching power, and this process in course of time superseded all the old methods of bleaching by chlorine.
It has been recently surmised that the action of light upon nitrate of silver formed the subject of discussion at the Lunar Society, and of experiments by Boulton and Watt but we find no indications of this in their correspondence. They were so unreserved with each other on all matters of business as well as science that, had any phenomena of so remarkable a character as those which have issued in the art of photography become known to either Boulton or Watt, we feel confident that they must have formed the subject of much personal discussion, and of many written communications. But both correspondents are alike entirely silent on the subject and we infer that no such experiments were made by them, or, if made, that they led to no results! 
Among the many foreigners who were attracted by this distinguished circle of scientific men, we find M. Faujas-Saint-Fond, who visited Birmingham in the course of his tour in England in 1785, while the circle was as yet unbroken, and Watt, Boulton, Priestley, and the rest, were in the full tide of business, invention, and inquiry. Saint-Fond had the pleasure of dining one day with Watt when Dr. Priestley was present, and describes in glowing terms the interest of their conversation. "Watt," he says, "joins to the frankness of a Scotchman the amiability and kindness of a man of the world. Surrounded by charming children, well educated and full of talent, he enjoys in their midst the happiness of regarding them as his friends, while he is almost worshipped by them as the best of fathers." A subsequent visit which be paid to Dr. Priestley in company with Dr. Withering, leads him to describe the philosopher's house at Fairhill, then about a mile and a half from Birmingham. "It is," he says, "a charming residence, with a fine meadow on one side, and a beautiful garden on the other. There was an air of perfect neatness about the place within and without." He describes the Doctor's laboratory, in which he conducted his experiments, as "situated at the extremity of a court, and detached from the house to avoid the danger of fire."
"It consists of several apartments on the ground floor. On entering it, I was struck with the sight of a simple and ingenious apparatus for making experiments on inflammable gas extracted from iron and water reduced to vapour. It consisted of a tube, tolerably long and thick, made out of one piece of copper to avoid soldering. The part exposed to the fire was thicker than the rest. He introduced into the tube cuttings or filings of iron, and instead of letting the water fall into it drop by drop, he preferred introducing it as vapour. The furnace was fired by coke instead of coal, this being the best of combustibles for intensity and equality of heat. . . . Dr. Priestley kindly allowed me to make a drawing of his apparatus for the purpose of communicating it to the French chemists who are engaged in the same investigations as himself. . . . The Doctor has embellished his rural retreat with a philosophical cabinet, containing all the instruments necessary for his scientific labours; as well as a library, containing a store of the most valuable books. He employs his time in a variety of studies. History, moral philosophy, and religion, occupy his attention by turns. An active, intelligent mind, and a natural avidity for knowledge, draw him towards the physical sciences; but a soft and impressible heart again leads him to religious and philanthropic inquiries. . . . I had indeed the greatest pleasure in seeing this amiable savant in the midst of his books, his furnaces, and his philosophical instruments; at his side an educated wife, a lovely daughter, and in a charming residence, where everything bespoke industry, peace, and happiness." 
Only a few years after the date of this visit, while Priestley was still busied with his chemical investigations, his house at Fairhill, thus described by Saint-Fond, was invaded by a brutal mob, who ruthlessly destroyed his library, his apparatus, and his furniture, and forced him to fly from Birmingham, glad to escape with his life.
The Lunar Society continued to exist for some years longer. But one by one the members dropped off. Dr. Priestley emigrated to America; Dr. Withering, Josiah Wedgwood, and Dr. Darwin, died before the close of the century and, without them, a meeting of the Lunar Society was no longer what it used to be. Instead of an assembly of active, inquiring men, it was more like a meeting of spectres with a Death's head in the chair. The associations connected with the meeting reminding the few lingering survivors of the losses of friends became of too painful a character to be kept alive and the Lunar Society, like the members of which it was composed, gradually expired. Its spirit, however, did not, die. The Society had stimulated inquiry, and quickened the zeal for knowledge of all who had come within the reach of its influence; and this spirit diffused and propagated itself in all directions. Leonard Horner, who visited Soho in 1809, thus referred to the continued moral influence of the association:— "The remnant of the Lunar Society," he says, "and the fresh remembrance in others of the remarkable men who composed it, are very interesting. The impression which they made is not yet worn out, but shows itself, to the second and third generation, in a spirit of scientific curiosity and free inquiry, which even yet makes some stand against the combined forces of Methodism, Toryism, and the love of gain."