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eses of mankind, but of the greatest practical importance, though the leading fact was already known.

Fortunately for Dr. Black, and for the world, he had now gotten a pupil who was as keenly interested in this scientific question as the professor. This was Mr. James Watt, then employed in fitting up the instruments in the M'Farlane Observatory of the university; a philosopher, in the most exalted sense of the word, who never could be satisfied with a conjectural knowledge of any subject, and who grudged no labour or study to acquire certainty in his researches. He chanced to have in his hands, for repairs, a model of Newcomen's steam-engine, belonging to the Natural Philosophy class, and was delighted with the opportunity which this small machine gave him for trying experiments connected with the theory of ebullition, which he had just learned from Dr. Black. These he prosecuted in a most happy train of success, and did not stop, till his steam-engine was rendered more like the most docile of animals, than a frame of lifeless matter; so that, while its power is competent to the lifting a house from its place, a child of ten years old shall, with a touch of his hand, make it go fast or slow, forwards or backwards, and act either powerfully or feebly. This gentleman, attached to Dr. Black by every tie of respect, esteem, and affection, supplied him with proofs and illustrations in abun dance, of all the points on which the professor wanted information. These were always recited in the class, with the most cordial acknowledgment of obligation to Mr. Watt. Mr. Irvine, also, a young student of medicine, of a quick apprehension, sound understanding, and particularly disposed to consider every thing mathematically, was at this time a hearer of Dr. Black's lectures, and greatly captivated with chemical science. He engaged, with great pleasure and zeal, in all examinations which seemed to interest the professor, and particularly such as would admit of mathematical consideration-thermometrical experiments on the scale of heat ;on the connection between expansion and variation of temperature; on the measures of heat, &c. ;-all these were fields of research altogether to his mind. He supplied Dr. Black with a vast number of experiments on the equilibrium of heat, on the specific heats of different substances, and on the continued absorption and fixation of heat by glass, sealing-wax, resin, and other substances, which gradually become more fluid. The register of these experiments are in my possession, and are similar to those which now fill many pages of the Memoires of the Foreign Academies,' P. xliii,

Mr. Robison enlarges very satisfactorily on the importance of Dr. Black's doctrine, and the consequences to be drawn from it, in the explanation of the various phænomena of nature. In 1966, Dr. Cullen was appointed professor of the Institutes of Medicine, and Dr. Black was invited from Glasgow, to succeed him in the chemical chair. Had it depended,' observes the biographer, on the university, he would have been appointed to this office on the death of Dr. Plummer,

though so shortly after his graduation; but of this not the slightest evidence appears. The following remarks we have already alluded to.

• Such a man was of the highest value to a celebrated seminary of learning. Ingenious men, of a fertile and lively imagination, are but too apt to give a loose to their fancy, in forming widegrasping theories, and dressing them out in specious attire. The young student, ardent and credulous, is dazzled by what appears a strong and wide-spreading light, not remarking that perhaps it is not the natural emanation from a luminary, but is artificially collected by mirrors and glasses; or that what he takes for real objects are only the shadowy representations by a magic lanthorn. To this, in a great measure, may we ascribe the continual flux of theory which may be observed in all universities. Yet the consequences to science are most unfortunate. Not only do the precious years of youth and of mental energy pass on without solid instruction, but also the most unfortunate of all habits is acquired, that of considering the extensive and plausible application of a theory to the explanation of phenomena as a valid proof of its truth. But, on the other hand, the lectures of such a teacher as Dr. Black, never permitting this play of fancy, and even rarely introducing conjecture, would be safe lessons for ingenuous youth. The affirmations of the professor may be trusted as matter of experience, and the student will acquire betimes the habit of never proceeding, in research of any kind, without sounding the channel as he ad

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Dr. Black was appointed to the chemical chair at Edinburgh, to the general satisfaction of the public; but the university of Glasgow thence sustained an irreparable loss. In this new scene, his talents were more conspicuous, and more extensively useful. He saw this; and while he could not but be highly gratified by the great concourse of pupils, which the reputation of the medical colleges of Edinburgh brought to his lectures, his mind was forcibly impressed by the importance of his duties as their teacher. This had an effect, of which it is difficult to say whether it has been fortunate for the public or not. Dr. Black now formed the firm resolution of directing his whole study to the improvement of his scholars in the elementary knowledge of chemistry. He saw too many of them with a very scanty stock of previous learning. He had many from the workshop of the manufacturer, who had none at all; and he saw that the number of such hearers must increase with the increasing activity and prosperity of the country: and these appeared to him as by no means the least important part of his auditory. To engage the attention of such pupils, and to be perfectly understood by the most illiterate, was therefore considered by Dr. Black as his most sacred duty. Plain doctrines, therefore, taught in the plainest manner, must employ his chief study. That no help may be wanting, all must be illustrated by suitable experiments, by the exhibition of specimens, and the management of chemical processes. Nice and abstruse philosophical opinions would not interest such hearers; and any doctrines, inculcated in a

refined manner, and referring to elaborate disquisitions of others, would not be understood by the major part of an audience of young persons, as yet only beginning their studies.' P. xlix.

Mr. Robison next gives a general and pleasing view of the progress of pneumatic chemistry, and accounts for the continued inactivity of Dr. Black in these researches, from the weak state of his health, and the frequent necessity of relaxation of thought, as well as of gentle exercise. The nume

rous inquirers into the nature of gases borrowed freely, with little acknowledgement, from our professor; though he has in no instance retorted, or even claimed his own productions. Some disingenuity in Lavoisier roused him to exertion; but was the hectic of the moment: the angry passions had decayed, or never existed; and we are told that not a trace of resentment or ill-will remained.

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What were the instructions of Dr. Black at Edinburgh, and what was his mode of life, are sufficiently known. Mild, gentle, benevolent, and communicative, he seemed more than or dinarily happy when he could assist, entertain, or instruct. With a few friends of peculiar talents; with the esteem of all those who knew, and were able to appreciate, his abilities and virtues; with the universal regard of those whom nothing more than his name and character had reached, he lived with comfort, and ceased to breathe-for death had none of its attendant struggles or pains-when the last thread of a feeble constitution would support life no longer.

I have already observed, that when I was first acquainted with Dr. Black, his aspect was comely and interesting. As he advanced in years, his countenance continued to preserve that pleasing expression of inward satisfaction, which, by giving ease to the beholder, never fails to please. His manner was perfectly easy, and unaffected, and graceful. He was of most easy approach, affable, and readily entered into conversation, whether serious or 'trivial. His mind being abundantly furnished with matter, his conversation was at all times pertinent and agreeable: for Dr. Black's acquirements were not merely those of a man of science. He was a stranger to none of the elegant accomplishments of life. He therefore easily fell into any topic of conversation, and supported his part in it respectably. He had a fine or accurate musical ear, and a voice which would obey it in the most perfect manner; for he sung, and performed on the flute, with great taste and feeling; and could sing a plain air at sight, which many instrumental performers cannot do.. But this was science. Dr. Black was a very intelligent judge of musical composition; and I never heard any person express so intelligibly the characteristic differences of some of the national musics of Europe. I speak of Dr. Black as I knew him at Glasgow: after his coming to Edinburgh, he gave up most of those amusements. Without having studied drawing, he had acquired a considerable power of expression with

his pencil, both in figures and in landscape. He was peculiarly happy in expressing the passions; and seemed, in this respect, to have the talent of a history painter. He had not had any opportuni ties of becoming a connoisseur; but his opinion of a piece of paint ing, or sculpture, was respected by good judges. Figure, indeed, of every kind, attracted his attention;-in architecture, furniture, ornament of every sort, it was never a matter of indifference. Even a retort, or a crucible, was to his eye an example of beauty or deformity. His memorandum books are full of studies (may I call them) of this sort; and there is one drawing of an iron-furnace, fitted up with rough anhewn timber, that is finished with great beauty, and would not disgrace the hand of a Woollet. Naturally, therefore, the young ladies were proud of Dr. Black's approbation of their taste in matters of ornament. These are not indifferent things; they are features of an elegant mind, and they account for some part of that satisfaction and pleasure which persons of all different habits and pursuits felt in Dr. Black's com pany and conversation.' P. lxvi.

Ilis only works were his Thesis de Acido a Cibis orto e de Magnesia; his Experiments on Magnesia, Quick-lime, and other alkaline Substances, published in the second volume of the Physical and Literary Essays of Edinburgh, 1756; Observations on the more ready Freezing of Water that has been boiled, published in the Philosophical Transactions, 1774; and The Analysis of the Waters of some of the boiling Springs of Iceland, in the Edinburgh Transactions. The Observations on Magnesia, &c. were, we believe, published separately at a subsequent period.

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We lately remarked, that the definition of chemistry has been a subject of much difficulty, and some contest. Dr. Black, after examining the definitions of different authors, observes, that the chemist studies the effects produced by heat and mixture in all bodies, or mixtures of bodies, natural or artificial, and studies them with a view to the improvement of arts, and the knowledge of nature.' It is not proper, at this time, to commence a verbal controversy; but we think the definition exceptionable. The object of a science is not, justly, a part of its definition; and the term mixture' does not, in common language, imply composition. What we suggested in the last number of our Second Series, p. 379, will more perfectly discriminate the science of chemistry. We there supposed it to comprehend the doctrine of the mutual action of the smaller particles of matter, either in decomposing natural bodies, or producing new compounds." Dr. Black objects to the synthetic form of teaching this science on a different foundation from that on which we restedour opposition. He thinks chemistry by no means advanced to such a state of perfection as to admit of general principles. It must still be pursued by analysis.

As the extent of our article will not permit us at present to enlarge on the work itself, we shall add the author's general design, in his own words, from one of his introductory lectures preserved in the notes.

There is just now a rage for system,-for complete systems. We have got such a high conceit of our knowledge, that we cannot be pleased with a system which acknowledges any imperfection: it must not leave one open link: it must not leave any thing unexplained. And I see it always happen that if the application of a system to the explanation of phenomena be very comprehensive, leaving no blanks, and if the explanation have some feasibility, this catches the fancy,-it dazzles the understanding. Nay, we think it impossible that a principle that is false can tally with so many phenomena. This seeming coincidence is considered as a proof of its validity; and we are no longer solicitous about the direct proofs adduced in the beginning. I have often heard such arguments for what I knew to be great nonsense. This kind of authority accruing to a theory from its specious and extensive application to phenomena, is always bad; and, with mere beginners in philosophy, it is doing them an irreparable hurt. It nourishes that itch for theory; and it makes them unsolicitous about the first foundations of it;-thus it forms in their minds the worst of all philosophical habits.

I am resolved to go on in a very different way. I subscribe to almost all Mr. Lavoisier's doctrines; and I will teach them all. And I affirm that I shall teach them with an impression of their truth which his method can never make. My students shall get all these doctrines piece-meal;-every one of them by steps which shall be quite easy and confident, because they shall be acquainted with every substance before I employ its phenomena as proofs. Each of Mr. Lavoisier's doctrines shall arise in course, as a small and obvious addition to the properties of some substance already known. Then I shall carry the student back, and shew him that the influence of our new discovery extends also to those substances which we had been considering before. Thus, all the doctrines will be had easily, familiarly, and with confidence in their truth.

I even think that this method will be more pleasant,-the novelties, or reformations, being, by this method, distributed over the whole course. And it will have yet another advantage: it will make the student acquainted with the chemistry of former years, which is far from being unworthy of the attention of a philosopher. Newton, Stahl, Margraaf, Cramer, Scheele, Bergmann, were geniuses not below the common level. But the person who learns chemistry by Lavoisier's scheme may remain ignorant of all that was done by former chemists, and unable to read their excellent writings.' P. 548.

We need not apologise for the length of this quotation: the observations are truly excellent. The work itself we shall soon again resume.

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