« ElőzőTovább »
some neighbouring stream, absorbed all his thoughts when the sheep were going astray, and the cattle were devouring or treading down the corn. His mother was soon convinced that he never would shine as a farmer, and she therefore very wisely determined that he should be allowed to follow the natural bent of his mind, and she sent him to Trinity College, Cambridge, into which he was admitted on the 5th of June, 1660, in the eighteenth year of his age.
It is strange enough, that the delusions of judicial astrology seem first to have led his mind to the study of mathematics, which at once enabled him to detect the falsehood of that flattering imposture. Without any assistance from his tutor, he made himself master of Descartes's Geometry; in 1664, he purchased a prism for the purpose of testing that philosopher's theory of colours ; in 1669, he succeeded his friend, Dr. Barrow, as Lucasian professor of mathematics, and it was then that he may be said to have entered upon that course of discovery which has ennobled his name. The first of these appears in the grand conclusion, which he drew from a series of prismatic experiments," that light was not homogeneous, but consisted of rays, some of which were more refrangible than others.” This discovery he immediately applied to the improvement of optical instruments, and although he did not succeed in rendering them as complete as he wished, nevertheless, he laid down principles, by means of which chiefly, those instruments have since been brought to a wonderful degree of perfection. Dr. Brewster gives a detailed account of the different stages of excellence through which the manufacture of telescopes gradually passed, until they were taken up by the Herschels and the Dollonds, for which we must refer the reader to the volume itself. We cannot, however, omit one melancholy fact which he states, but for which we cannot agree with him in thinking that the government is blameable. After mentioning the gigantic telescope, forty feet long, with a speculum forty-nine and a half inches in diameter, which was finished by Dr. Herschel in 1789, under the patronage of George III., he proceeds to say:
· The genius and perseverance which created instruments of such transcendent magnitude were not likely to terminate with their construction. In the examination of the starry heavens, the ultimate object of his labours, Dr. Herschel exhibited the same exalted qualifications, and in a few years he rose from the level of humble life to the enjoyment of a name more glorious than that of the sages and warriors of ancient times, and as immortal as the objects with which it will be for ever associated. Nor was it in the ardour of the spring of life that these triumphs of reason were achieved. Dr. Herschel had reached the middle of his course before his career of discovery began, and it was in the autumn and winter of his days that he reaped the full harvest of his glory. The discovery of a new planet at the verge of the solar system was the first trophy of his skill, and new double and multiple stars, and new nebulæ, and groups of celestial bodies, were added in thousands to the system of the universe. The spring tide of
knowledge which was thus let in upon the human mind, continued for a while to spread its waves over Europe ; but when it sank to its ebb in England, there was no other bark left upon the strand but that of the Deucalion of Science, whose home had been so long upon its waters.
During the life of Dr. Herschel, and during the reign, and within the dominions of his royal patron, four new planets were added to the solar system, but they were detected by telescopes of ordinary power; and we venture to state, that since the reign of George II), no attempt has been made to keep up the continuity of Dr. Herschel's discoveries.
* Mr. Herschel, his distinguished son, has indeed completed more than one telescope of considerable size ;-Mr. Ramage, of Aberdeen, has executed reflectors rivalling almost those of Slough ;-and Lord Oxmantown, an Irish nobleman of high promise, is now engaged on an instrument of great size. But what avails the enthusiasm and the efforts of individual minds in the intellectual rivalry of nations ? When the proud science of England pines in obscurity, blighted by the absence of the royal favour, and of the nation's sympathy;—when its chivalry fall unwept and unhonoured ;-how can it sustain the conflict against the honoured and marshalled genius of foreign lands?'-pp. 35-37.
It is undoubtedly much to be lamented that no systematic measures have been adopted for keeping up the continuity of Dr. Herschel's discoveries.' But we should like to know for what
purpose we have such an institution as the Royal Society, if it possess neither the means nor the disposition to accomplish objects of this nature ? Unhappily, personal jealousies exercise a great deal too much influence upon that body, and in many instances, we fear, wholly paralyse their faculties. Of this society Newton became a member in 1672; and it was against some of its most distinguished members that he had to contend with all the energies of his mind, in order to establish the simple and beautiful theory of light which he had first discovered. * Such was the rancorous and personal style in which they carried on their controversies against him, that he was at length disgusted not only with the men, but with the very researches which brought upon him so much of their bitterness and odium. Is it not mortifying to our nature to read in one of his letters addressed, towards the close of 1675, to Leibnitz, such a sentence as the following one ?-"I was so persecuted with discussions arising from the publication of my theory of light, that I blamed my own imprudence for parting with so substantial a blessing as my quiet to run after a shadow.” This and many similar complaints had Newton to make chiefly against the members of the Royal Society, who were already envious of his rising fame, at the very time when he was engaged in laying before that body some of the most interesting parts of his doctrine of colours, which he had deduced from his prismatical experiments. The leading points of that doctrine, as popularised by Dr. Brewster, may be shortly stated :
• If the objects of the material world had been illuminated with white light, all the particles of which possessed the same degree of refrangibility,
and were equally acted upon by the bodies on which they fall, all nature would have shone with a leaden hue, and all the combinations of external objects, and all the features of the human countenance, would have. exhibited no other variety but that which they possess in a pencil sketch or a China-ink drawing. The rainbow itself would have dwindled into a narrow arch of white light,--the stars would have shone through a grey sky,—and the mantle of a wintry twilight would have replaced the golden vesture of the rising and the setting sun. But he who has exhibited such matchless skill in the organization of material bodies, and such exquisite taste in the forms upon which they are modelled, has superadded that ethereal beauty which enhances their more permanent qualities, and presents them to us in the ever-varying colours of the spectrum. Without this the foliage of vegetable life might have filled the eye and fostered the fruit which it veils, but the youthful green of its spring would have been blended with the dying yellow of its autumn. Without this the diamond might have displayed to science the beauty of its forms, and yielded to the arts its adamantine virtues ;—but it would have ceased to shine in the chaplet of beauty, and to sparkle in the diadem of princes. Without this the human countenance might have expressed all the sympathies of the heart, but the “ purple light of love” would not have risen on the cheek, nor the hectic flush been the herald of its decay.
* The gay colouring with which the Almighty has decked the pale marble of nature, is not the result of any quality inherent in the coloured body, or in the particles by which it may be tinged, but is merely a property of the light in which they happen to be placed. Newton was the first person who placed this great truth in the clearest evidence. He found that all bodies, whatever were their peculiar colours, exhibited these colours only in white light. When they were illuminated by homogenous red light they appeared red, by homogenous yellow light, yellow, and so on, “their colours being most brisk and vivid under the influence of their own daylight colours." The leaf of a plant, for example, appeared green in the white light of day, because it had the property of reflecting that light in greater abundance than any other. When it was placed in homogenous red light, it could no longer appear green, because there was no green light to reflect; but it reflected a portion of red light, because there was some red in the compound green which it had the property of reflecting. Had the leaf originally reflected a pure homogenous green, unmixed with red, and reflected no white light from its outer surface, it would have appeared quite black in pure homogenous red light, as this light does not contain a single ray which the leaf was capable of reflecting. Hence the colours of material bodies are owing to the property which they possess of stopping certain
rays of white light, while they reflect or transmit to the eye the rest of the rays of which white light is composed.-pp. 78–80.
It would be beside the object of this article to enter with any degree of minuteness into the various optical researches of Newton, particularly those of a minor description, in which his mind was engaged, or rather amused, for some years. There is, however, one deduction at which he arrived, by the process of close philosophical reasoning, which bears some slight analogy, from its simplicity, as well as its truth, to the grander proportions which he was after
wards enabled, by a similar process, to establish in astronomy, and which, therefore, we shall notice in passing. One of the nicest problems in optics is, to distinguish the forces
which reflect from those which refract light. Newton found by experiment, that those forces are very nearly proportional to the densities of the bodies on which the
rays of light fall, with the exception of unctuous and sulphureous bodies, such as camphor, olive oil, linseed oil, spirit of turpentine, and diamond, which have their refractive powers two or three times greater in respect of their densities than the other substances in the table, while among themselves their refractive powers are proportional to their densities, without any considerable variation.' Hence, Newton concluded, without any assistance from chemistry, that diamond " is an unctuous substance coagulated,” an abstract inference, the truth of which has since been demonstrated by actual experiments, a summary of which we shall here subjoin, from Mr. Murray's curious memoir on the diamond :
“ The event has amply verified this conjecture, and the Tuscan philosophers and the Honourable Mr. Boyle ascertained the fact. The first grand experiment to prove the combustibility of the diamond took place in the presence of Cosmo III., Grand Duke of Tuscany, wherein the diamond being exposed in the focus of the great lens (still in the Grand Duke's laboratory at Florence), it was entirely volatilized. Guyton de Morveau, and others, consumed the diamond, and it was readily dissipated in the focus of the great inirror of Tchirnhausen, as we believe it subseqently was in that of Parker’s burning lens. In the year 1771, Macquer observed the diamond to inflame. Guyton de Morveau had proved that the diamond was destroyed when projected into red-hot nitre; and it was also burnt by means of melted nitre in a gold tube, by Mr. Tennant. When fragments of diamond were introduced into the brilliant arch of flame, evolved between points of charcoal in the galvanic batteries of the Royal Institution, consisting of 2000 double plates, and exposing a surface of 128,000 square inches, they rapidly disappeared, being completely volatilized. The diamond may be easily consumed by being placed in a cavity of charcoal, and urging on it the flame of a spirit lamp, by means of a stream of oxygen.
“So far the combustibility of the diamond was completely ascertained, but its nature remained still undetermined. Lavoisier had proved and pointed out that carbonic acid gas was evolved as a product both in the combustion of the diamond and that of charcoal, and thus their identity was inferred. The researches of Clouet, Messrs. Allen and Pepys, and others, have confirmed this conclusion. Sir George Mackenzie converted iron into steel by powdered diamonds. Mr. Children's immense battery consisted of twenty triads, each six feet long, by two feet eight inches broad, exposing a total surface of thirty-two feet; when iron, with diamond powder interposed, was exposed to its influence, the iron was converted into steel, and the diamond disappeared ; and Mr. Smithson Tennant, having placed a diamond in a gold tube, supported in a state of incandescence, a stream of oxygen, by means of gentle pressure, was made to traverse it, and the result proved that the oxygen was transformed into an equal volume of
carbonic acid gas, which was found in an opposite receiver resting over mercury. Sir Humphry Davy, when at Florence, made some experiments with the Grand Duke's burning lens, on the combustion of the diamond. He found that when the gem was introduced into a glass globe, supplied with
oxygen, and kindled by the lens, it continued to burn after it was removed from the focus—the oxygen was supplanted by an equal volume of carbonic acid gas, while there was no deposit of aqueous vapour.
On the other hand, when plumbago and charcoal were consumed under similar circumstances, there was a sensible diminution of volume, and also a formation of watery vapour, clearly proving that the latter contained hydrogen.* Experiment has thus unequivocally demonstrated that the diamond is pure crystallized Carbon.”-pp. 16–18.
But the pedestal upon which Newton's fame chiefly rests, and from which it never can be shaken, is composed of his astronomical discoveries, those transcendent deductions' as Dr. Brewster justly styles them, of human reason, by which he has secured to himself an immortal name, and vindicated the intellectual dignity of his species.' It would be unjust to affirm, that for these signal achievements, Newton was indebted solely to his own faculties and researches. Great is the merit undoubtedly of several of the distinguished astronomers by whom he was preceded, and by whose labours his way may be said to have been cleared, and renowned especially are the memories of Copernicus, Tycho Brahe, Kepler, and Galileo, of whose contributions to the science the author has given compendious sketches, which are executed in his happiest style, and add greatly to the variety and value of this little work. From Copernicus, Newton learned the arrangement and general movements of the planetary bodies; from Tycho Brahe, the inequality of the moon's motion ; from Kepler, the motion of the planetary bodies in elliptical orbits, and from Galileo, the whole system of planets of the secondary order. The question still remained to be solved, what was the principle that gave motion to the heavenly bodies, and retained them in those paths from which they are not known ever to have deviated, since they have been first observed by the eye of man? Some astronomers said it was the principle of attraction: Newton demonstrated that it was gravitation, and it is this discovery that has encompassed his name with a halo of never-fading glory.
Driven from Cambridge by the plague in the year 1666, he happening to be sitting alone in his garden at Woolsthorpe, when, to follow the popular story, he saw an apple fall from a tree. The incident turned his attention to the nature of gravity, and he reflected on that remarkable power which causes all bodies to descend towards the centre of the earth. This power he found to be as operative at the tops of the highest mountains, as at the bottoms of the deepest mines; he therefore conceived that it must extend
* Phil. Trans. Part II. 1814.'