PHLOGISTON

99

matter to light we can pour that element out of one vessel 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."

In the following year (March 21, 1782) we find Priestley also writing to Wedgwood:

"Before my late experiments, phlogiston was indeed almost given up by the Lunar Society, but now it seems to be reestablished."

How difficult it was to convince Priestley may be seen from the following extract from a letter to his friend Franklin, who was then in Paris, written at about the same time :

"BIRMINGHAM, June 24, 1782.

"Please to inform the Duc de Rochefoucauld, whose civilities to me I remember with pleasure, that my experiments are certainly inconsistent with Mr Lavoisier's supposition of there being no such thing as phlogiston, and that it is the addition of air, and not the loss of anything, that converts a metal into a calx. In their usual state calces of metals do not contain air, but that may be expelled by heat, and after this I reduce them to a perfect metallic state by nothing but inflammable air, which they imbibe in toto, without any decomposition. I lately reduced 101 ounce measures of this air to two by calx of lead, and that small remainder was still inflammable. I explain Mr Lavoisier's experiments by supposing that precipitate per se [mercuric oxide] contains all the phlogiston of the metal mercury, but in a different state; but I can show other calces which also contain more phlogiston than the metals themselves. That mercury in its metallic state does contain phlogiston or inflammable air is evident from the production of nitrous air by the solution of it in spirits of nitre, and I make nitrous air from nothing but nitrous vapour and inflammable air; so that it indisputably consists of these two ingredients. I have already ascertained

G

the proportion of inflammable air that enters into the composition of lead, tin, copper and silver, and am proceeding with the other metals as fast as I can. When the whole is completed I shall give you a further account of it.

"I am exceedingly concerned to find that it is so difficult a thing to make peace; but I hope before the campaign is over all parties will have had enough of war, and be sensible that they will gain nothing by continuing it. If I had any voice in the business, the prospect of seeing you in this country would be a strong additional motive to accelerate the negotiations.

"With the greatest respect and every good wish.—I am, dear sir, yours sincerely, J. PRIESTLEY.'

There were already many indications prior to 1780 that men were beginning to be troubled as to the sufficiency of Stahl's generalisation to account for the rapidly-accumulating mass of facts which the application of quantitative chemistry to the study of natural phenomena was bringing to light. Priestley's advent in Birmingham certainly retarded by the weight of his authority the growth in heterodoxy in that particular among the members of the Lunar Society, and indirectly therefore all whom they could influence.

The following letter from Keir is typical of many which passed between the members of the Society in reference to Priestley's work and of the discussions which it occasioned.

KEIR TO PRIESTLEY.

"The more we discover of Nature, the further we are removed from the conceit of our being able to understand the operations. "I wish M. Berthollet and his associates would relate their facts in plain prose, that all men might understand them, and reserve their poetry of the new nomenclature for their theoretical commentaries on the facts.

of

"I have wished much to call on you to hear of the progress your experiments, but have been much indisposed with the

rheumatism. I long to know what acids you get with the other inflammable airs. If you get different acids from the inflammable air made from sulphur and water, that made from marine acid and copper (for I would avoid iron on account of its plumbago and carbon), and that made from charcoal and water :-I say, if these acids are different (suppose, according to my notions, vitriolic, marine and fixed air), then will you not be obliged to admit that there is not one inflammable but many inflammables, which opinion you now think as heterodox as the Athanasian System.

"However, there are wonderful resources in the dispute about Phlogiston, by which either party can evade, so that I am less sanguine than you are in my hopes of seeing it terminated. One consolation remains, that in your experiments you cannot fail of discovering something perhaps of as great or greater importance for us to know."

Nevertheless, even in the Club itself there was at least one man who came under the influence of Priestley, but who eventually emancipated himself, and this was Withering, who, we are informed, read to them "a humorous piece in verse entitled The Life and Death of Phlogiston,' which was long remembered for its clever treatment and pointed wit."

That Priestley's influence still reigned in the Club, even down to 1803, may be inferred from the introduction to his essay, "The Doctrine of Phlogiston Established"-the last of his scientific papers-in which he says, "And now that Dr Crawford is dead, I hardly know of any person, except my friends of the Lunar Society of Birmingham, who adhere to the doctrine of Phlogiston."

As regards the history of the Lunar Society there is little more to tell. One by one its members submitted themselves to the arrest of the "fell sergeant," and eventually Keir, Watt, and Boulton, the founder, were

the only survivors, and its meetings were gradually discontinued.

"But," says its historian, "the influence exerted by the Society did not die; it had stimulated inquiry and quickened the zeal for knowledge of all who had come within its influence, and this spirit diffused and propagated itself in all directions."

Leonard Horner, who visited Soho in 1809, thus refers 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 Toryism and the love of gain."

CHAPTER VIII

Priestley at Birmingham-His theological work thereHis love of literature-His catholicity-His personal characteristics.

IN 1784 Priestley brought out a revised edition of the work on which his fame as a man of science mainly rests, under the title of " Experiments and Observations on Different Kinds of Air; and other branches of Natural Philosophy connected with the Subject. In three volumes, being the former six abridged and methodised. With many Additions. London, 1790. 3 vols. 8vo." In a letter to his friend Keir we find an allusion to this matter. He says:

"I am working like a horse at the new arrangements of my 6 vols. of Experiments. It is a tedious business.

"What do you think of an attempt to dedicate this work to the Prince of Wales? The King I shall never think of in any such light, nor the Prince, unless it be possible that he will be a real patron of science and could look upon it in some other light than that of an honour to myself."

An interesting account of Priestley at this period of his life is to be found in the Memoirs of the French geologist, Faujar St Fond, who visited Birmingham some time after Priestley's settlement there. He says:

He

"Dr Priestley received me with the greatest kindness. presented me to his wife and his daughter, who were distinguished by vivacity, intelligence and gentleness of manner. The young lady spoke to me of one of her brothers, who was then finishing his education at Geneva and to whom she seemed very much attached.

"The building in which Dr Priestley made his chemical and philosophical experiments was detached from his house to avoid