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"The Republic has no need of chemists; the course of justice cannot be suspended," was the reply.
On the 8th of May 1794, the guillotine did its work; and in his fifty-first year Lavoisier "joined the majority." To the honour of the Academy of which he was so ill.u.s.trious a member it is recorded that a deputation of his fellow-workers in science, braving the wrath of Robespierre, penetrated to the dungeons of the prison and placed a wreath on the grave of their comrade.
The period of the infancy of chemical science which I have now briefly described is broadly contemporaneous with the second half of the eighteenth century.
At this time the minds of men were greatly stirred. Opinions and beliefs consecrated by the a.s.sent of generations of men were questioned or denied; the pretensions of civil and ecclesiastical authorities were withstood; a.s.sertions however strongly made, and by whatever authority supported, were met by demands for reasons. In France this revolt against mere authority was especially marked. Led by the great thinker Voltaire, the French philosophers attacked the generally accepted views in moral, theological and historical matters. A little later they began to turn with eager attention and hope to the facts of external Nature. Physical science was cultivated with wonderful vigour and with surprising success.
In the sciences of heat and light we have at this time the all-important works of Fourier, Prevost and Fresnel; in geology and natural history we have Buffon and Cuvier; the name of Bichat marks the beginning of biological science, and chemistry takes rank as a science only from the time of Lavoisier.
From the philosophers an interest in natural science spread through the ma.s.s of the people. About the year 1870 the lecture-rooms of the great teachers of chemistry, astronomy, electricity, and even anatomy were crowded with ladies and gentlemen of fashion in the French capital. A similar state of matters was noticeable in this country. Dr. Black's lecture theatre was filled by an audience which comprised many young men of good position. To know something of chemistry became an essential part of the training of all who desired to be liberally educated.
The secrets of Nature were now rapidly explored; astonishing advances were made, and as a matter of course much opposition was raised.
In this active, inquiring atmosphere the young science of chemistry grew towards maturity.
Priestley, ever seeking for new facts, announcing discovery after discovery, attacking popular belief in most matters, yet satisfied to interpret his scientific discoveries in terms of the hypothesis with which he was most familiar, was the pioneer of the advancing science. He may be compared to the advance-guard sent forward by the explorers of a new country with orders to clear a way for the main body: his work was not to level the rough parts of the way, or to fill in the miry places with well-laid metal, but rather rapidly to make a road as far into the heart of the country as possible.
And we have seen how well he did the work. In his discovery of various kinds of airs, notably of oxygen, he laid the basis of the great generalizations of Lavoisier, and, what was perhaps of even more importance, he introduced a new method into chemistry. He showed the existence of a new and unexplored region. Before his time, Hooke and Mayow had proved the existence of more than one kind of air, but the chemistry of gases arose with the discoveries of Priestley.
Although Black's chief research, on fixed air and on latent heat, was completed fifteen or twenty years before Priestley's discovery of oxygen, yet the kind of work done by Black, and its influence on chemical science, mark him as coming after Priestley in order of development. We have seen that the work of Black was characterized by thoroughness and suggestiveness. The largeness of scope, the breadth of view, of this great philosopher are best ill.u.s.trated in his discourses on heat; he there leads us with him in his survey of the domain of Nature, and although he tells us that hypotheses are a "mere waste of time," we find that it is by the strength of his imagination that he commands a.s.sent. But he never allows the imagination to degenerate into fanciful guesses; he vigorously tests the fundamental facts of his theory, and then he uses the imagination in developing the necessary consequences of these facts.
To Black we owe not only the first rigorously accurate chemical investigation, but also the establishment of just ideas concerning the nature of heat.
But Lavoisier came before us as a greater than either Priestley or Black.
To great accuracy and great breadth of view he added wonderful power of generalizing; with these, aided by marked mental activity and, on the whole, favourable external circ.u.mstances, he was able finally to overthrow the loose opinions regarding combustion and elementary principles which prevailed before his time, and so to establish chemistry as one of the natural sciences.
At the close of the first period of advance we find that the sphere of chemistry has been defined; that the object of the science has been laid down, as being to find an explanation of the remarkable changes noticed in the properties of bodies; that as a first step towards the wished-for explanation, all material substances have been divided by the chemist into elements and compounds; that an element has been defined as any kind of matter from a given weight of which no simpler forms of matter--that is, no kinds of matter each weighing less than the original matter--have as yet been obtained; that the great principle of the indestructibility of matter has been established, viz. that however the properties of matter may be altered, yet the total ma.s.s (or quant.i.ty) remains unchanged; and lastly, we find that an explanation of one important cla.s.s of chemical changes--those changes which occur when substances burn--has been found.
And we have also learned that the method by which these results were obtained was this--to go to Nature, to observe and experiment accurately, to consider carefully the results of these experiments, and so to form a general hypothesis; by the use of the mental powers, and notably by the use of the imagination, to develop the necessary deductions from this hypothesis; and finally, to try these deductions by again inquiring from Nature "whether these things were so."
Before the time which we have been considering the paths of chemical science had scarcely yet been trodden. Each discovery was full of promise, each advance displayed the possibility of further progress; the atmosphere was filled as with "a mighty rushing wind" ready to sweep away the old order of things. The age was an age of doubt and of freedom from the trammels of authority; it was a time eminently suited for making advances in natural knowledge.
In the unceasing activity of Priestley and Lavoisier we may trace the influence of the restlessness of the age; but in the quietness and strength of the best work of these men, and notably in the work of Black; in the calmness with which Priestley bore his misfortunes at Birmingham; in the n.o.ble words of Lavoisier, "I am not unwilling to part with life, but I ask time to finish my experiments, because the results will, I believe, be for the good of humanity"--we see the truth of the a.s.sertion made by one who was himself a faithful student of Nature--
"Nature never did betray The heart that loved her."
 The translation is taken from Thomson's "History of Chemistry."
 Nevertheless, in other places Lavoisier most readily acknowledges the merits of Priestley.
 A similar method of reasoning was employed so far back as the tenth century: thus, in an Anglo-Saxon "Manual of Astronomy" we read, "There is no corporeal thing which has not in it the four elements, that is, air and fire, earth and water.... Take a stick and rub it on something, it becomes hot directly with the fire which lurks in it; burn one end, then goeth the moisture out at the other end with the smoke."
ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL SCIENCE--PERIOD OF DALTON.
_John Dalton_, 1766-1844.
The progress of chemical knowledge became so rapid in the early years of the present century, that although I have in this chapter called the time immediately succeeding that of Lavoisier "the period of John Dalton," and although I shall attempt to describe the advances made by this philosopher without considering those of his contemporaries Davy and Berzelius, yet I must insist on the facts that this arrangement is made purely for the sake of convenience, and that many of the discoveries of Davy, Berzelius and others came in order of time before, or followed close upon the publication of Dalton's atomic theory.
Nevertheless, as the work of these men belongs in its essence to the modern period, and as the promulgation of the atomic theory by Dalton marks the beginning of this period, it seems better that we should have a clear conception of what was done by this chemist before proceeding to consider the advances made by his contemporaries and successors.
JOHN DALTON, the second of three children of Joseph and Deborah Dalton, was born at Eaglesfield, a village near c.o.c.kermouth, in c.u.mberland, on the 5th of September 1766. One of the first meeting-houses established by the Society of Friends is to be found in Eaglesfield.
The Dalton family had been settled for several generations on a small copyhold estate in this village. The first of them to join the Friends was the grandfather of John Dalton; his descendants remained faithful adherents of this society.
Dalton attended the village schools of Eaglesfield and the neighbourhood until he was eleven years old, by which time, in addition to learning reading, writing and arithmetic, he had "gone through a course of mensuration, surveying, navigation, etc." At the age of ten his taste for measurements and calculations began to be remarked by those around him; this taste was encouraged by Mr. Robinson, a relative of Dalton, who recognizing the indomitable perseverance of the boy appears to have taken some care about this time in directing his mathematical studies.
At the early age of twelve Dalton affixed to the door of his father's house a large sheet of paper whereon he announced that he had opened a school for youth of both s.e.xes; also that "paper, pens and ink" were sold within.
The boy-teacher had little authority over his pupils, who challenged their master to fight in the graveyard, and broke the windows of the room into which they had been locked till their tasks should be learned.
When he was fifteen years old Dalton removed to Kendal, where he continued for eleven or twelve years, at first as a.s.sistant-master, and then, along with his elder brother Jonathan, as princ.i.p.al of a boarding school for boys.
It was announced by the brothers that in this school "youth will be carefully instructed in English, Latin, Greek and French; also writing, arithmetic, merchants' accounts and the mathematics." The school was not very successful. Both brothers were hard, inflexible, and ungainly in their habits, and neither was fitted to become a successful teacher of boys: of the two, John had the gentler disposition, and was preferred by the boys; "besides, his mind was so occupied by mathematics that their faults escaped his notice."
During this time Dalton employed his leisure in learning Latin, Greek and French, and in pursuing his studies in mathematics and natural philosophy.
He became a frequent contributor to the _Gentlemen's Diary_, a paper which received problems of various kinds--chiefly mathematical--and presented prizes for their successful solution.
Besides setting and answering mathematical problems in this journal, and also in the _Ladies' Diary_, Dalton sometimes ventured into the wider fields of mental phenomena. It seems strange to read that, even at the age of twenty-six, Dalton should occupy his leisure time composing answers to such queries as these:--
"Whether, to a generous mind, is the conferring or receiving an obligation, the greater pleasure?"
"Is it possible for a person of sensibility and virtue, who has once felt the pa.s.sion of love in the fullest extent that the human heart is capable of receiving it (being by death or some other circ.u.mstance for ever deprived of the object of its wishes), ever to feel an equal pa.s.sion for any other object?"
In his answer to the second of these queries, Dalton carefully framed two hypotheses, and as carefully drew conclusions from each. The question in the _Diary_ was by "Mira;" if "Mira" were a "rapturous maiden" she would not derive much comfort from the cold and mathematical answer by "Mr. John Dalton of Kendal."
At Kendal Dalton made the acquaintance of Mr. Gough, who was about eight years older than Dalton, and had been blind from the age of two. Mr. Gough, we are a.s.sured by Dalton, was "a perfect master of the Latin, Greek and French tongues;" he understood "well all the different branches of mathematics;" there was "no branch of natural philosophy but what he was well acquainted with;" he knew "by the touch, taste and smell, almost every plant within twenty miles of Kendal." To the friendship of this remarkable man Dalton owed much; with his help he acquired a fair knowledge of the cla.s.sical languages, and he it was who set Dalton the example of keeping a regular record of weather observations.
On the 24th of March 1787 Dalton made his first entry in a book which he ent.i.tled "Observations on the Weather, etc.;" the last entry in this book he made fifty-seven years later on the evening preceding his death. The importance of Dalton's meteorological observations, as leading him to the conception of the atomic theory, will be noticed as we proceed.
In the year 1793 Dalton, who was now twenty-seven years of age, was invited to Manchester to become tutor in the mathematical and natural philosophy department of a college recently established by influential Dissenters in that town. Eighty pounds for the session of ten months was guaranteed him; and he was provided with "rooms and commons" in the college at a charge of 27 10_s._ per session.
He held this appointment for six years, when he retired, and continuing to live in Manchester devoted himself to researches in natural philosophy, gaining a living by giving private lessons in mathematics and physical science at a charge of 2_s._ 6_d._ per hour, or 1_s._ 6_d._ each if more than two pupils attended at the same time.
Dalton was elected a Fellow of the Literary and Philosophical Society of Manchester in the year 1794; and from the time of his retiring from the tutorship of Manchester New College till the close of his life he spent a great part of his time in a room in the society's house in George Street, in studying and teaching. The fifty years thus spent are marked by few outward events. The history of Dalton's life from this time is the history of the development of his intellect, and the record of his scientific discoveries.
On one occasion during Dalton's stay at Kendal, as he was about to make a visit to his native village, he bethought himself that the present of a pair of silken hose would be acceptable to his mother. He accordingly purchased a pair marked "newest fashion;" but his mother's remark, "Thou hast brought me a pair of grand hose, John; but what made thee fancy so light a colour? I can never show myself at meeting in them," rather disconcerted him, as to his eyes the hose were of the orthodox drab colour.
His mother insisted that the stockings were "as red as a cherry." John's brother upheld the "drab" side of the dispute; so the neighbours were called in, and gave their decision that the hose were "varra fine stuff, but uncommon scarlety."