570 SPECIAL METHODS OF DISCOVERY. continual inclination towards the point, ping, or & south.' It was by observation that Robert Norman discovered, in 1576, the dip of a magnet. Julius Cæsar, a surgeon at Rimini, observed in the year 1590, that iron was converted into a magnet by position alone. Professor Gunter, of Gresham College, was the first to observe, in the year 1622, the change of declination of a magnet in the same. place. Gassendi also, by means of observation, discovered about the year 1630, that an iron bar which had long remained in one position, and had been struck by lightning, had become a magnet. In the year 1633, Gallibrand discovered by observation that the amount of variation of the magnetic needle at London was not constant. Professor Wargentin observed, in the year 1750, that the northern aurora affected the magnetic needle. In 1778, Brugmans discovered by experiment and observation, that bismuth and antimony were each repelled by the poles of a magnet. About the year 1805, Romagnesi observed that a magnetised needle experiences a declination when submitted to the action of a voltaic current.2 In 1806, Humboldt, at Berlin, observed and discovered the existence of magnetic storms. Arago was the first to observe and discover, in 1824, the retarding influence of substances, metals in particular, upon the movements of an adjacent magnetic needle. By means of observation, comparison, and inference, Sabine, in 1851, discovered that the sun is a great magnet, and magnetises our earth, because the terrestrial magnetic force has periods respectively of 24 hours, 365 days, and 10 solar years.3 3 1 See Sir W. Snow Harris, Rudimentary Magnetism, part iii. p. 80; Davis, The Chinese, pp. 277, 278; also Mrs. Somerville, Connexion of the Physical Sciences, 2nd edit. p. 334. 2 See Manuel du Galvanisme, par Joseph Izarn, Paris, 1805, p. 120 ; also Journal of the Society of Arts, April 23, 1858, p. 356. 3 See Encyclopædia Britannica, 8th edit., art. Magnetism,' p. 18. It was by observing the action of substances upon each other, with and without the application of heat, that many of the ordinary tests in chemical analysis were discovered. Many of the discoveries also in geology, mineralogy, anatomy, the action of medicines, &c., have resulted from the ordinary use of the observing faculty. Gaspard Asellius, Professor of Anatomy at Pavia, discovered, by observation, in 1622, the lacteal vessels, which convey food to the blood; and Jean Pacquet, in 1647, by further observation discovered that those vessels pour the nutriment into the thoracic duct. In the early part of the seventeenth century also, and whilst the celebrated anatomist Harvey was his pupil, Professor Fabricius Aquapendente, of Padua, discovered by observation, that many of our veins contain valves, which lie open as long as the blood is flowing towards the heart; and it was a knowledge of this fact which led Harvey towards his great discovery of the circulation of the blood. It was largely by means of observations of different kinds taken during his extensive travels, that Humboldt made his numerous discoveries in terrestrial physics and natural history, the tracing of isothermal lines (i.e. those of equal temperature) over this globe; the existence of green plants living in perfect darkness in the mines at Freyberg, &c. &c. William Scoresby, about the year 1816, discovered by sailing to the 80th parallel of latitude, that the water was free from ice over a space of 18,000 square miles. Agassiz also, by means largely of observation, became a great discoverer of glacier phenomena, and found what were the chief signs, such as erratic blocks of stone, glacial drifts, scratchings, and moraines, by means of which the previous existence of ancient glaciers might be inferred; and that the northern parts of Europe and America were at one time covered with fields of ice. It was by observation that Brewster discovered the existence of fluids under a state of great pressure in stones, which caused the latter to explode whilst being cut. b. By employing new or improved modes or instruments of observation.-The method of making discoveries by means of the invention and employment of a new or improved mode of observation, is a very varied and extensive one, and has proved one of the most fruitful. It includes a number of more special ones: for instance, by using a new instrument of observation; by employing a known instrument in a new way; by using instruments of increased power or magnitude; by employment of improved, more exact, or more delicate instruments. Probably more discoveries have been made by means of this, than by any other equally special method, because it is highly adapted to several of the chief laws of discovery. A new mode of observation agrees with one of those laws 1 by enabling us to perceive matter and its phenomena in a new aspect; and as many of the phenomena of bodies are such as cannot be perceived at all by our unaided senses, the employment of a new or more delicate apparatus or mode of observing usually enables us to notice what we could not previously detect. Every new mode or instrument of observation, and every improvement in scientific apparatus, is almost invariably quickly followed by new discoveries. With every addition to the power of telescopes, more and more distant worlds have been discovered, and an increased number of supposed nebulæ have been found to be composed of numerous points of light. The use of microscopes of increased magnifying power and definition, has always been attended by discoveries of structures or markings still more minute; that of spectroscopes of increased dispersive power has also led to the discovery of a greater 1 See p. 458. DISCOVERY BY MEANS OF NEW MODES OF OBSERVATION. 573 number of bands in various spectra. By the use also of electrometers and galvanometers of increased delicacy, new sources of free electricity and of electric currents have frequently been revealed. It was by means of astronomical instruments of greatly increased accuracy that Tycho Brahe, in the latter part of the sixteenth century, was enabled to make an immense number of new observations. Galileo, in 1611, by employing a new instrument (the telescope) discovered the moons of Jupiter, but in consequence of the defective power or insufficient delicacy of the instrument, mistook Saturn's rings for two stars; and Huyghens, in 1659, by employing more accurate lenses, discovered the ring and one of the satellites of that planet. It was by means of the more accurate measurement and observation of an arc of the meridian in France, by Picard, in the year 1670, that Newton was enabled to verify the hypothesis and discover the law of universal gravitation in its action with regard to our moon. Savart, by adopting Lichtenberg's device of strewing powders upon plates, discovered that the vibrations artifically produced in a plate of bi-axial crystal, indicated the existence of varying elasticity in varying directions."1 Ritter, by employing the novel plan of using papers wetted with a solution of nitrate of silver, and allowing the solar spectrum to fall upon it in the dark, in the year 1801, discovered the dark chemical rays in solar beams. Wollaston's reflecting goniometer also, being a great improvement upon that of Romé de Lisle, the measurements obtained by it being more accurate the smaller the faces of the crystal (because the angles were measured by means of the reflected images of bright objects seen in them), enabled many new truths to be discovered which could not 1 Jevons, Principles of Science, vol. ii. p. 364. 574 SPECIAL METHODS OF DISCOVERY. otherwise have been found. It was by means of much more refined apparatus that Fraunhofer, of Munich, was enabled to observe and discover 576 dark lines in the solar spectrum, although Wollaston, by means of the prism, had previously found only seven. Airy also, by adopting a modified mode of observation, discovered that all the different varieties of polarised light might be obtained by means of rock-crystal, according to the direction in which the ray was transmitted, and that a crystal of quartz is capable of exhibiting every variety of elliptical polarisation of light. It was by the use of a more sensitive thermo-electric pile than the original one of Seebeck, that Melloni was enabled to make his discoveries in diathermancy. By means of the very greatly increased delicacy of the spectroscope as an instrument of chemical analysis over that of previous chemical tests, Swan was enabled to detect the widely diffused presence of excessively minute quantities of common salt.1 It was by the assistance also of greatly increased sensitiveness of the galvanometer which he employed, that Du Bois Reymond was enabled to make his discoveries of electric currents in animal tissues. As the molecular phenomena of nature are extremely. minute in comparison with the power of the senses, and we are acquainted only with the more crude existences and actions, it is probable that much of the discovery of the future will be effected by means of still greater refinements and powers of our apparatus and means of observation. c. By means of more intelligent and acute observation. Although this cannot be properly classed as a different method, it is so common an occurrence that I venture to place it under a separate heading. Many discoveries have been made by attentively observing effects. which would otherwise have passed unnoticed; for it is 1 See p. 179. |