In the eighth “Encyclopædia Britannica” (Vol. IV. p. 246), treating of the height of polar lights, reference is made to the extraordinary aurora borealis observed by Dalton on the 29th of March 1826, and of which a description is given in a paper read before the Royal Society, April 17, 1828 (Phil. Mag. or Annals, Vol. IV. p. 418; Philosophical Transactions for 1828, Part II; James Hoy in Phil. Mag., Vol. LI. p. 422; J. Farquharson in Phil. Trans. for 1839, p. 267). This aurora was seen in places one hundred and seventy miles apart and covered an area of 7000 to 8000 square miles. In Vol. XIV of the same Encyclopædia will be found (p. 15), an account of another aurora observed at Kendal, February 12, 1793, while at p. 12 are given Dalton’s views as to the connection between the heat and magnetism of the earth, and, at p. 66, his conclusions as to the cause of the aurora and its magnetic influence.
References.—“Memoirs of Dalton’s Life,” by Dr. W. C. Henry, London, 1854; “Life and Discoveries of Dalton,” in British Quarterly Review, No. 1; Pharmaceutical Journal, London, October 1841; Thomson’s “History of Chemistry,” Vol. II; Young’s “Course of Lectures,” London, 1807, Vol. I. pp. 706–709, 753, and Vol. II. pp. 466–470; Noad, “Manual,” etc., London, 1859, pp. 226, 269, 534; article, “Aurora Borealis,” immediately following A.D. 1683; Sir H. Davy, “Bakerian Lectures,” London, 1840, pp. 322, 323, 328–330; “Dict. of Nat. Biog.,” Vol. XIII. pp. 428–434, as well as the numerous references therein cited. Consult also, for theories, investigations, observations, records, etc., of the Aurora Borealis: Georg. Kruger, 1700; J. J. Scheuchzer, 1710–1712, 1728–1730; L. Feuillée, 1719; J. L. Rost, 1721; J. C. Spidberg, 1724; W. Derham, 1728, 1729–1730; F. C. Mayer—Meyer, 1726; J. F. Weidler, 1729, 1730, 1735; J. Lulolfs, 1731; M. Kelsch, 1734; F. M. Zanotti, 1737, 1738; also Zanotti and P. Matteucci, 1739; B. Zendrini, J. Poleni, F. M. Serra, E. Sguario and D. Revillas in 1738; G. Bianchi, 1738 and 1740; J. M. Serantoni, 1740; G. C. Cilano de Maternus, 1743; S. von Trienwald, 1744; G. Guadagni, 1744; J. F. Ramus, 1745; C. Nocetus, 1747; P. Matteucci, 1747; Jno. Huxham, 1749–1750; G. W. Krafft, 1750; P. Kahm—Kalm, 1752; G. Reyger, 1756; A. Hellant, 1756, 1777; Jos. Stepling, 1761; H. Hamilton, 1767, 1777; M. A. Pictet, 1769; J. E. Silberschlag, 1770; C. E. Mirus, 1770; J. E. B. Wiedeburg, 1771; Max. Hell, 1776; Mr. Hall, J. H. Helmuth, 1777; E. H. de Ratte, W. L. Krafft, 1778; J. E. Helfenzrieder, 1778; G. S. Poli, 1778–1779; Marcorelle and Darguier, 1782; L. Cotte, 1783; J. A. Cramer, 1785; D. Galizi, in A. Calogera’s “Nuova Raccolta ...” Vol. XXXIX. p. 64; J. L. Boeckmann, in “Mem. de Berlin” for the year 1780; H. Ussher, 1788; G. Savioli, 1789, 1790; J. J. Hemmer, 1790; P. A. Bondoli, 1790, 1792, 1802; A. Prieto, 1794; J. D. Reuss’s works published in Göttingen; Jacopo Penada, 1807–1808; M. Le Prince, “Nouvelle Théorie ...”; W. Dobbie, 1820, 1823; Col. Gustavson, in Phil. Mag. for 1821, p. 312; M. Dutertre, 1822; J. L. Späth, 1822; Chr. Hansteen, 1827, 1855; L. F. Kaemtz, 1828, 1831; G. W. Muncke, 1828; J. Farquharson, 1829; D. Angelstrom, Rob. Hare, 1836; Ant. Colla, 1836, 1837; L. Pacinotti, 1837; G. F. Parrot, 1838; J. H. Lefroy, 1850, 1852; Don M. Rico-y-Sinobas, 1853; A. A. de La Rive, 1854; A. Boué (Katalog), 1856, 1857; C. J. H. E. Braun, 1858; E. Matzenauer, 1861; F. Dobelli, 1867; F. Denza, 1869.
A.D. 1793–1797.—Robison (John), a very distinguished English natural philosopher, completes what are without question the most important of all his scientific publications. These are to be found throughout the eighteen volumes and two supplements to the third “Encyclopædia Britannica,” where they cover such subjects as Physics, Electricity, Magnetism, Thunder, Variation, etc. etc. Taken together, “they exhibited,” according to Dr. Thomas Young, “a more complete view of the modern improvements of physical science than had previously been in the possession of the British public.”
It was after his retirement from the navy that Robison devoted himself to scientific studies, becoming the successor of Dr. Black in the lectureship of chemistry at the University of Glasgow during 1766, and accepting, seven years later (1773), the Professorship of Natural Philosophy at Edinburgh, where he taught all branches of physics and of the higher mathematics. In 1783 he was made Secretary of the Philosophical Society of Edinburgh, received the degree of Doctor of Laws, 1798–1799, and was elected foreign member of the Saint Petersburg Academy of Sciences in 1800. Of him, Mr. James Watt wrote, Feb. 7, 1805: “He was a man of the clearest head and the most science of anybody I have known” (Arago’s “Eloge of Jas. Watt,” London, 1839, p. 81).
It was while acting as midshipman under Admiral Saunders that Robison himself observed the effect of the aurora borealis on the compass, which had been remarked by Hiörter, Wargentin, and Mairan several years before, but which was not then generally known. The aurora borealis, he afterwards wrote, “is observed in Europe to disturb the needle exceedingly, sometimes drawing it several degrees from its position. It is always observed to increase its rate of deviation from the meridian; that is an aurora borealis makes the needle point more westerly. This disturbance sometimes amounts to six or seven degrees, and is generally observed to be greatest when the aurora borealis is most remarkable.... Van Swinden says he seldom or never failed to observe aurora borealis immediately after any anomalous motion of the needle, and concluded that there had been one at the time, though he could not see it.... This should farther incite us to observe the circumstance formerly mentioned, viz., that the South end of the dipping needle points to that part of the heavens where the rays of the aurora borealis appear to converge....”
The experiments of J. H. Lambert (at A.D. 1766–1776) upon the laws of magnetic action were carefully repeated by Robison, who, in 1769 or 1770, tried various methods and made numerous investigations from which he deduced that the force is inversely as the square of the distance. When he observed, however, some years afterward, that Æpinus had in 1777 conceived the force to vary inversely as the simple distance, he carefully again repeated the experiments and added others made with the same magnet and with the same needle placed at one side of the magnet instead of above it. By this simple arrangement the result was still more satisfactory, and the inverse law of the square of the distance was well established.
Throughout his numerous investigations, Prof. Robison found that when a good magnet was struck for three-quarters of an hour, and allowed in the meantime to ring, its efficacy was destroyed, although the same operation had little effect when the ringing was impeded; so that the continued exertion of the cohesive and repulsive powers appears to favour the transmission of the magnetic as well as of the electric fluid. The internal agitation, produced in bending a magnetic wire around a cylinder, also destroys its polarity, and, it is said, the operation on a file has the same effect. M. Cavallo found that brass becomes generally much more capable of being attracted when it has been hammered, even between two flints; and that this property is again diminished by fire: in this case, Dr. Thomas Young remarks, it may be conjectured that hammering increases the conducting power of the iron contained in the brass, and thus renders it more susceptible of magnetic action.
Of his other very important observations in the same line it would be difficult to select the most interesting, and it may suffice to call attention merely to such as are noted throughout Prof. Alfred M. Mayer’s valuable contributions on “The Magnet, Magnetism,” etc., in Johnson’s “New Universal Encyclopædia,” as well as in his “Practical Experiments in Magnetism,” etc., published through the columns of the Scientific American Supplement.
Prof. Robison’s electrical investigations are scarcely less interesting. In the theories advanced by Æpinus and Cavendish it was shown that the action of the electrical fluid diminished with the distance, while M. Coulomb proved, by a series of elaborate experiments, that it varied like gravity in the inverse ratio of the square of the distance. Robison had previously determined that in the mutual repulsion of two similarly electrified spheres the law was slightly in excess of the inverse duplicate ratio of the distance, while in the attraction of oppositely electrified spheres the deviation from that ratio was in defect; and he therefore arrived at the same conclusion formed by Lord Stanhope, that the law of electrical attraction is similar to that of gravity.
At the close of Richard Fowler’s “Experiments and Observations,” etc., Edinburgh, 1793, is a letter from Prof. Robison, wherein he gives the following results of many curious investigations, mostly made upon himself, to ascertain the effects of the galvanic influence. He found the latter influence well defined on applying one of two metallic substances to a wound which he had accidentally received; discovered by their tastes the solders in gold and silver trinkets; and showed that the galvanic sensation can be felt when the metallic substances are placed at a distance from each other. He proved the last-named fact by placing a piece of zinc between one of the cheeks and the gums, and a piece of silver on the opposite side within the other cheek. He next introduced a zinc rod between the piece of zinc and the cheek on the one side, and a silver rod between the silver and the cheek on the other, and when he afterward carefully brought into contact the extremities of the rods outside the mouth a flash appeared and a powerful sensation was noticeable in the gums. He experienced the same sensation when he again separated the rods and brought them to a short distance from each other, but he could perceive no galvanic effect when he placed the rods (or wires) in such manner that the silver rod should touch the zinc or the zinc rod touch the piece of silver. He also ascribed to galvanic effect the well-known fact that the drinking of porter out of a pewter pot produces a more brisk sensation than when it is taken out of a glass vessel. In this instance, he says there is a combination of one metal and of two dissimilar fluids. In the act of drinking, one side of the pewter pot is exposed to the saliva and the humidity of the mouth, while the other metallic side is in contact with the porter. In completing the circuit, in the act of drinking, a brisk and lively sensation arises, which imparts an agreeable relish to the liquid. He likewise observed that the conducting power of silk thread depends greatly on its colour, or rather on the nature of its dye. When of a brilliant white, or a black, its conducting power is the greatest; while either a high golden yellow or a nut-brown renders it the best insulator. Human hair, when completely freed from everything that water could wash out of it, and then dried by lime and coated with lac, was equal to silk.