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through life one of its most useful and valuable associates.

At this time the whole range of chemical and physico-chemical science
was in an extremely imperfect state; and the first steps to a more
improved system involved the necessity of clearing away a vast mass of
error which encumbered the path to truth. For instance, one of the
fanciful ideas, the offspring of the alchemy of the dark ages, which
still continued to haunt the regions of science, was the belief of the
conversion of water into earth by gradual consolidation. This subject
Lavoisier treated in the true spirit of the experimental method, and
clearly showed that the pretended conversion was either a deposition of
earthy particles, or a sediment arising from the action of the water on
the internal surface of the retort. He also laboured on the analysis of
the gypsum found in the neighbourhood of Paris, and on the
crystallization of salts. He discussed the project of conveying water
from L’Yvette to Paris, and the theory of congelation; and to these
researches added extensive observations on the phenomena of thunder and
the Aurora Borealis.

He next directed his attention more especially to mineralogy; and made
excursions, in conjunction with Guettard, into all parts of France,
endeavouring to form from different districts a complete collection of
their characteristic mineral productions. He made advances towards a
systematic classification of facts connected with the localities of
fossils, which afterwards served as the basis of his work on the
revolutions of the globe and the formation of successive strata, of
which two admirable abstracts were inserted in the Memoirs of the
Academy of Sciences, for 1772 and 1787.

Thus during the earlier part of his life, Lavoisier does not seem to
have devoted himself in particular to any one branch of science. But
about the year 1770 the announcement of the existence of more than one
species of gaseous matter, arising out of the successive researches of
Black, Scheele, Priestley, and Cavendish, had the effect of fixing his
attention to the subject of pneumatic chemistry. The invaluable
discoveries just alluded to had opened a new world to the inquirer into
nature; and the labours of those distinguished experimentalists had
conspired to commence a fresh era in science. Lavoisier was one of the
first to appreciate at once the importance of the results they had
arrived at, and the immense field of further research to which those
results had opened the way. He perceived by a sort of instinct the
glorious career which lay before him; and the influence which this new
science thus, as it were, created, must have over every sort of physical
research. Priestley possessed precisely those qualifications which are
most available for striking out new and brilliant discoveries of facts;
a boundless fertility of invention; a power of rapidly seizing remote
analogies; and an equal readiness in framing and in abandoning
hypotheses, which have no value, but as guides to experiment. Lavoisier,
less eminent in these respects, possessed in a more peculiar degree the
mental characteristics which enable their owner to advance to grand
generalizations and philosophical theories upon the sure basis of facts.
He possessed, in its fullest sense, the true spirit of inductive
caution, and even geometrical rigour; and his observations, eminently
precise and luminous, always pointed to more general views.

In 1774, he published his ‘Opuscules Chimiques,’ in which, after a full
and truly philosophical examination of the labours of preceding
experimenters in the discovery of the gases and their characteristic
properties, he proceeds to describe his own beautiful and fundamentally
important researches, from which resulted the ‘True Theory of
Combustion,’ which may be termed the very sun and centre of the whole
modern system of chemistry.

To the vague dreams of the alchemist had succeeded the remarkable theory
of Hooke, who maintained that a certain ingredient of the atmospheric
air (which also enters as an ingredient into several other bodies,
especially nitre) was the _solvent_ which absorbed a portion of the
combustible. This process was continued in proportion as more of the
solvent was supplied. The solution took place with such rapidity, as to
occasion those motions or pulsations in which Hooke believed heat and
light to consist.

This near approach to the truth was thrown into discredit by the more
brilliant and imposing theory of Stahl, who captivated the imaginations
of chemists by his doctrine of phlogiston, the principle or element of
fire, a sort of metaphysical something, which conferred the property of
being combustible. Stahl taught that the process of combustion deprived
bodies of their phlogiston, which, in the act of separation, exhibited
its latent energies in the evolution of light and heat.

This wild chimera long maintained its ground, and received successive
modifications in the hands of several distinguished chemists, the most
important of which was that of Kirwan; but these all retained the
fundamental error that something was _abstracted from_ the burning body.
Yet Rey, so early as 1630, and Bayer afterwards, had both shown that
metals by calcination _increase_ in weight, or have something _added_ to
them. Lavoisier turned his attention to the defects of the existing
theory about 1770; and the last-named experiments probably directed him
more specifically to the essential point of the inquiry. He pursued his
researches with unwearied industry; and by a long series of experiments
of the most laborious and precise nature, he succeeded in determining
that, in all cases of combustion, that substance which is the _real_
combustible invariably receives _an addition_, or enters into a new
combination; and the matter with which it combines is in all cases that
same substance which had now been shown by Priestley to be one of the
constituents of the atmosphere, and which was then known by the name of
_vital air_.

It was however long before Lavoisier gained a single convert. At length
M. Berthollet, at a meeting of the Academy in 1785, publicly renounced
the old opinions and declared himself a convert. Fourcroy followed his
example. In 1787, Morveau, during a visit to Paris, became convinced,
and declared the conclusions of Lavoisier irresistible. The younger
chemists speedily embraced the new views; and their establishment was
thus complete. There only remained some lurking prejudices in England,
where the Essay of Kirwan retained its credit. Lavoisier and his
coadjutors translated this essay into French, accompanying each section
by a refutation. So completely was this done, that the author himself
was convinced; and, with that candour which distinguishes superior
minds, gave up his views as untenable, and declared himself a convert.

These discoveries introduced Lavoisier to the notice of the most eminent
persons in the State; and in 1776, Turgot engaged him to superintend the
manufacture of gunpowder for the Government. He introduced many valuable
improvements in the process, and many judicious reforms into the

In 1778, Lavoisier having been incessantly engaged on the subject of
gases and combustion, announced another great discovery, “that the
respirable portion of the atmosphere is the constituent principle of
acids,” which he therefore denominated _oxygen_.

The question as to “the acidifying principle” had long formed the
subject of discussion. The prevalent theory was that of Beccher with
various modifications, which made the acid principle a compound of earth
and water regarded as elements. Lavoisier found in the instance of a
great number of the acids, that they consisted of a combustible
principle united with oxygen. He showed this both analytically and
synthetically, and hence proceeded to the conclusion that oxygen is the
acidifying principle in all acids. Berthollet opposed this doctrine, and
contended that, in general, acidity depended on the manner and
proportion in which the constituents are combined. The fact is, that, in
this instance, Lavoisier had advanced a little too rapidly to his
conclusion. Had he contented himself with stating it as applying to a
_great number_ of acids, it would have been strictly true; but he had
certainly no proof of its being _universally_ the case. When Sir H.
Davy, some years after, showed that one of the most powerful acids (the
muriatic) does not contain a single particle of oxygen, and when the
researches of Guy Lussac and others had exhibited other proofs of the
same thing, it became evident that Lavoisier’s assertion required
considerable modification. And though _nearly_ all acids have been since
included under the general law of containing _some supporter of
combustion_, yet there appear to be exceptions even to this; the
cautious language of Berthollet has been completely justified; and a
perfect theory of acidity is perhaps yet wanting. Nevertheless,
Lavoisier’s discovery is one of first-rate magnitude and importance, and
with this qualification, certainly forms the basis of all our present
knowledge of the subject.

Another important research in which Lavoisier engaged, in conjunction
with Laplace, was the determination of the specific heats of bodies, by
means of an ingenious apparatus, which they denominated the calorimeter:
these were by far the most precise experiments on the subject which had
as yet been made, though some inaccuracies in the method have since been
pointed out.

Lavoisier owed much, it must be owned, to those external advantages of
fortune, the absence of which, though it cannot confine the flights of
real genius, yet may seriously impair the value and efficiency of its
exertions; and the presence of which, though it cannot confer the powers
of intellect, may yet afford most invaluable aids to the prosecution of
research, and the dissemination of knowledge. In the instance before us,
these advantages were enjoyed to the full extent, and turned to the best
use. Lavoisier was enabled to command the most unlimited resources of
instrumental aid; he pursued his researches in a laboratory furnished
with the most costly apparatus, and was able to put every suggestion to
the test of experiment, by the assistance of the most skilful artists,
and instruments of the most perfect construction.

But as he could thus command these essential advantages for the
prosecution of his own investigations, he was equally mindful of the
extension of similar advantages to others: he always evinced himself
ready to assist the inquiries of those who had not the same means at
their disposal; and was no less liberal in aiding them by his stores of
information and able advice. Indeed no one could be more sensible how
much there is of mutual advantage in such intercourse between those
engaged in the same scientific labours; and this conviction, joined with
a full perception of the immense benefits accruing from personal
acquaintance among men of kindred pursuits, and the interchange of
social good offices, led him to the regular practice of opening his
house on two evenings in every week, for an assembly of all the
scientific men of the French capital; which very soon became a point of
general resort and reunion to the philosophers of Europe.

At these meetings general discourse and philosophic discussion were
agreeably intermingled; the opinions of the most eminent philosophers
were freely canvassed; the most striking and novel passages in the
publications of foreign countries were made known, recited, and
animadverted upon; and the progress of experiment was assisted by candid
comments and comparison with theory. In these assemblies might be found,
mingling in instructive and delightful conversation, all those whose
names made the last century memorable in the annals of science.
Priestley, Fontana, Landriani, Watt, Bolton, and Ingenhouz, were
associated with Laplace, Lagrange, Borda, Cousin, Monge, Morveau, and
Berthollet. There was also an incalculable advantage in bringing into
communication and intimacy men engaged in distinct branches of science:
the intercourse of the mathematician with the geologist, of the
astronomer with the chemist, of the computer with the experimenter, and
of the artist with the theorist, could not fail to be of mutual
advantage. In no instance were the beneficial effects of such
intercourse more strikingly displayed than in the chemical sciences;
which, from this sort of comparison of ideas and methods, began now to
assume a character of exactness from an infusion of the spirit of
geometry; and a department hitherto abandoned to the wildest
speculations, and encumbered with the most vague and undefined
phraseology (derived from the jargon of the alchemists), began to assume
something like arrangement and method in its ideas, and precision and
order in its nomenclature. This influence was strongly marked in the
physical memoirs produced in France from this period downwards. The
precision and severity of style, and the philosophical method of the
mathematicians, was insensibly transfused into the papers of the
physical and chemical philosophers.

Lavoisier individually profited greatly by the sources of improvement
and information thus opened. Whenever any new result presented itself to
him, which, perhaps, from contradicting all received theories, seemed
paradoxical, or at variance with all principles hitherto recognised, it
was fully laid before these select assemblies of philosophers; the
experiment was exhibited in their presence, and they were invited with
the utmost candour to offer their criticisms and objections. In perfect
reliance on the mutual spirit of candour, they were not backward in
urging whatever difficulties occurred to them, and the truth thus
elicited acquired a firmness and stability in its public reception
proportioned to the severity of the test it had undergone. Lavoisier
seldom announced any discovery until it had passed this ordeal.

At length he combined his philosophical views into a connected system,
which he published in 1789, under the title of ‘Elements of Chemistry:’
a beautiful model of scientific composition, clear and logical in its
arrangement, perspicuous and even elegant in its style and manner. These
perfections are rarely to be found in elementary works written by
original discoverers. The genius which qualifies a man for enlarging the
boundaries of science by his own inventions and researches is of a very
different class from that which confers the ability to elucidate, in a
simple and systematic course, the order and connexion of elementary
truths. But in Lavoisier these different species of talent were most
happily blended. He not only added profound truths to science, but
succeeded in adapting them to the apprehension of students, and was able
to render them attractive by his eloquence.

In 1791 he entered upon extensive researches, having for their object
the application of pneumatic chemistry to the advancement of medicine,
in reference to the process of respiration. With this view he examined
in great detail the changes which the air undergoes, and the products
generated in that process of the animal economy. He had previously,
however, as far back as 1780, detailed a series of experiments to
determine the quantity of oxygen consumed and carbonic acid generated by
respiration, in a given time, in the Memoirs of the French Academy.

In the twenty volumes of the Academy of Sciences, from 1772 to 1793, are
not less than forty memoirs by Lavoisier, replete with all the grand
phenomena of the science:—the doctrine of combustion in all its
bearings; the nature and analysis of atmospheric air; the generation and
combinations of elastic fluids; the properties of heat; the composition
of acids; the decomposition and recomposition of water; the solutions of
metals; and the phenomena of vegetation, fermentation, and
animalization. These are some of the most important subjects of his
papers; and during the whole of this period he advanced steadily in the
course which was pointed out to him by the unerring rules of inductive
inquiry, to which his original genius supplied the commentary. So well
did he secure every point of the results to which he ascended, that he
never made a false step. It was only in one subject, before alluded to,
that he may be said to have gone a few steps too far. Nor did he ever
suffer himself to be discouraged, or his ardour to be damped by the
difficulties and obstacles which perpetually impeded his progress. He
traced new paths for investigation, and founded a new school of science;
and his successors had ample employment in following out the inquiries
which he had indicated, and exploring those recesses to which he had
opened the way.

In the relations of social and civil life Lavoisier was exemplary; and
he rendered essential service to the state in several capacities. He was
treasurer to the Academy, and introduced economy and order into its
finances: he was also a member of the board of consultation, and took an
active share in its business. When the new system of measures was in
agitation, and it was proposed to determine a degree of the meridian, he
made accurate experiments on the dilatation of metals, in conjunction
with Laplace (1782), to ascertain the corrections due to changes of
temperature in the substances used as measuring rods in those delicate

By the National Convention he was consulted on the means of improving
the manufacture of assignats, and of increasing the difficulty of
forgery. He turned his attention to matters of rural economy, and, by
improved methods of cultivation, on scientific principles, he increased
the produce of an experimental farm nearly one half. In 1791 he was
invited by the Constituent Assembly to digest a plan for simplifying the
collection of taxes: the excellent memoir which he produced on this
subject was printed under the title of ‘The Territorial Riches of
France.’ He was likewise appointed a Commissioner of the National
Treasury, in which he effected some beneficial reforms.

During the terrors of Robespierre’s tyranny, Lavoisier remarked that he
foresaw he should be stripped of all his property, and accordingly would
prepare to enter the profession of an apothecary, by which he should be
able to gain a livelihood. But the ignorant and brutal ruffians who were
then in power had already condemned him to the scaffold, on which he was
executed, May 8, 1794, for the pretended crime of having adulterated
snuff with ingredients destructive to the health of the citizens! On
being seized, he entreated at least to be allowed time to finish some
experiments in which he was engaged; but the reply of Coffinhall, the
president of the gang who condemned him, was characteristic of the
savage ignorance of those monsters in human form:—“The Republic does not
want savans or chemists, and the course of justice cannot be suspended.”

Lavoisier in person was tall and graceful, and of lively manners and
appearance. He was mild, sociable, and obliging; and in his habits
unaffectedly plain and simple. He was liberal in pecuniary assistance to
those in need of it; and his hatred of all ostentation in doing good
probably concealed greatly the real amount of his beneficence. He
married, in 1771, Marie-Anni-Pierrette Paulze, a lady of great talents
and accomplishments, who after his death became the wife of Count



The celebrated physician, Thomas Sydenham, in many respects the most
eminent that England has produced, was born in the year 1624, at
Wynford-Eagle, in Dorsetshire, where his father, William Sydenham,
enjoyed a considerable estate. The mansion in which he was born is now
converted into a farm-house, and stands on the property of Lord Wynford.

In the year 1642, when eighteen, he was admitted as a commoner at
Magdalen-Hall, Oxford; but quitted it in the same year, when that city
became the head quarters of the royal army, after the battle of
Edge-hill. He was probably induced to take this step by reasons of a
political nature; for we find that his family were active adherents of
the opposite party. Indeed he is said, though on doubtful authority, to
have held a commission himself under the Parliament during his absence
from Oxford; and his elder brother, William, is known to have attained
considerable rank in the republican army, and held important commands
under the Protectorate.

The political bias of his family is not without interest, as affording a
probable explanation of some circumstances in his life which would
otherwise be rather unaccountable,—such as the fact, that though he
reached the first eminence as a practising physician, he was never
employed at court, and was slighted by the college, who invested him
with none of their honours, nor even advanced him to the fellowship,
though a licentiate of their body, and qualified by the requisite
University education.

When Oxford was surrendered to the Parliament, Sydenham determined to
resume his academical studies; and passing through London


_Engraved by E. Scriven._


_From the Picture in the Hall of All Souls College, Oxford._

Under the Superintendence of the Society for the Diffusion of Useful

_London, Published by Charles Knight, Ludgate Street._

on his way, he met accidentally with Dr. Thomas Coxe, a physician of
some repute at that time, who was attending his brother. The choice of a
profession became the subject of a conversation between them, which
determined him in favour of medicine; for in a letter addressed to Dr.
Mapletoft, thirty years after this time, which forms the preface to one
of his writings, he refers with much warmth to this conversation as the
origin of his professional zeal, and, consequently, of whatever useful
advances he had made in medicine. Thus his success, both in the practice
and reformation of his art, may show the advantage of waiting till the
faculties are fully matured, before they are exercised in a study which
requires independence as well as vigour in thinking: for the
circumstances of his family being sufficiently affluent to place him
above the necessity of choosing a profession early, he had not turned
his attention to physic till an age at which the medical education is
generally almost completed. We are not, however, to believe in the
justice of an accusation brought against him, that he had never studied
his profession till he began to practise it; for though we do not know
what particular line of study he pursued on his return to Oxford, it is
clear from many passages in his works that he had studied the writings
of the ancient physicians with no common care; and as his own show no
defect of acquaintance with whatever real information had been collected
before his time, we may reasonably conclude that this contemporary
censure was mistaken or malicious. He certainly held the opinions of his
modern predecessors in very little respect, for he does not often
mention them, even for the purpose of confutation; and in the letter to
Dr. Mapletoft already referred to, he says that he had found the best,
and, in fact, the only safe guide, through the various perplexities he
had met with in his practice, to be the method of actual observation and
experiment recommended by Lord Bacon. This sentiment is often repeated
in his works; but it surely does not countenance the idea that he had
begun to practise without endeavouring to make what preparation he
could, or would have had others follow such an example; for the charge
against him goes to this length. The notion might arise from a foolish
anecdote related by his admirer, Sir Richard Blackmore, of his having
recommended Don Quixote as the best introduction he knew to the practice
of medicine, which Sydenham must have intended as a jest, or perhaps as
a sarcasm on the narrator himself.

At Oxford he formed a close friendship with John Locke, better known
afterwards as a philosopher than as a physician. Their intimacy, which
lasted to the end of Sydenham’s life, probably contributed not a little
to give form to the disgust which he soon displayed at the
unsatisfactory and fluctuating state of medical opinion, and to the zeal
with which he sought to establish it on surer grounds; for he appeals,
as to the highest authority, in confirmation of some of his new views on
the treatment of fever, to the approval of his illustrious friend, who

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