Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/857

] tainly near enough to warrant some considerable suspicion of a physical connection.&quot; A longer period, during which the spot-maxima would seem to vary, has been suspected by Wolf. It was suggested by Mr Proctor in 1865, and Prof. Loomis (of Yale College, U.S.) has since advocated the theory, that this period corresponds to the successive conjunctions of Saturn and Jupiter; but the connection is doubtful.

Year. Days of Observation. Days without Spots. New Groups. 1826 277 22 118 1827 273 Z 161 1828 282 225 1829 244 199 1830 217 1 190 1831 239 3 149 1832 270 49 84 1833 267 139 33 1834 273 120 61 1835 244 18 173 1836 200 272 1837 168 333 1833 202 282 1839 205 162 1840 263 3 152 1841 283 15 102 1842 307 64 68 1843 312 149 34 1844 321 111 52 1845 332 29 114 1846 314 1 157 1847 276 257 1848 273 330 1849 285 238 1850 308 2 186 1851 303 141 1852 337 2 125 1853 299 4 91 1854 334 65 67 1855 313 146 28 1856 321 193 34 1857 324 52 93 1858 335 202 1859 343 205 1860 332 211 1861 322 204 1862 317 3 160 1863 330 2 124 1864 325 4 130 1865 307 26 93 1866 349 76 45 1867 312 195 25 1863 301 12 101 1869 195 224 1870 213 403 1871 219 271 1872 153 3 186

One of the most interesting results following Schwabe s great discovery was the recognition of an association between the sun-spot period and magnetic disturbances on the earth. Lamont of Munich had independently discovered, in 1850, that the mean daily range of the magnetic declination varies in a period of about ten years. Two years later, General Sabine and Professors Wolf and Gautier noted the coincidence of this period and that of the solar spots. Wolf afterwards proved that the true period of magnetic variation amounts to 11 11 years approximately. Some still regard the association between the sun-spot period and auroral phenomena as non-existent; but all doubt on the subject appears to be removed by the evidence adduced in two able papers by Professor Loomis (American Journal of Science and Arts, September 1870 and April 1873). In the same papers Professor Loomis indicates the evidence of association between the number of auroras observed each year, and the two orders of phenomena solar spots and magnetic variations. He remarks that, &quot; the auroral maximum generally occurs a little later than the magnetic maximum, the average difference amounting to one year; while the time of auroral minimum either coincides with the magnetic minimum or slightly precedes it, the average difference amounting to about half a year. On the whole,&quot; he proceeds, &quot;there seems to be no room for question that the number of auroras seen in the middle latitudes of Europe and America exhibits a true periodicity, following very closely the magnetic periods, but not exactly copying them. In particular, we notice that during those periods in which the range of the magnetic declination was unusually small auroral exhibitions were extremely few in number and in significant in respect of brilliancy. If now we inquire as to the probable connection between these three classes of phenomena, we cannot suppose that a small black spot on the sun exerts any direct influence on the earth s magnet ism or electricity ; but we must rather conclude that the black spot is a result of a disturbance of the sun s surface, which is accompanied by an emanation of some influence from the sun, which is almost instantly felt upon the earth, in an. unusual disturbance of the earth s magnetism, and a flow of electricity, developing the auroral light in the upper regions of the earth s atmosphere. The appearances favour the idea that this emanation consists of a direct flow of electricity from the sun. If we maintain that light and heat are the result of vibrations of a rare ether which fills all space, the analogy between these agents and electri city would lead us to conclude that this agent also is the result of vibrations in the same medium, or at least that it is a force capable of being propagated through the ether with a velocity similar to that of light. While this influ ence is travelling through the void celestial spaces it de velops no light ; but as soon as it encounters the earth s atmosphere, which appears to extend to a height of about 500 miles, it develops light, and its movements are con trolled by the earth s magnetic force, in a manner analogous to the influence of an artificial magnet upon a current of electricity circulating round it.&quot;

Among the most interesting discoveries in solar physics are those which have been effected by means of the spectroscopic analysis, not only as regards the constitution of the sun himself, but as to the nature of the solar spots and faculae, as well as of the various objects which lie outside the sun s visible surface, and are only rendered discernible during the darkness of total solar eclipses. The evidence of the spectroscope respecting the sun s constitution is too intimately associated with the history of spectroscopic analysis to be properly discussed at any length in this place. We propose, therefore, to present results, rather than to describe in detail the processes by which these results have been obtained, or the considera tions on which must be based the interpretation of such results. It has been shown, then, that the light of the sun comes from an orb glowing with intense white light, that is, light of all refrangibilities. Hence the sun is either liquid or solid, or if vaporous, then so greatly compressed that, in fact, the condition of its vapours is unlike that of any gases with which we are familiar. But inasmuch as the rainbow-tinted streak constituting the solar spectrum is crossed by a multitude of dark lines, it is seen that the glowing mass of the sun is surrounded by a complex vapour- ous envelope at a lower temperature. Nevertheless we are not to suppose that the vapours constituting the solar atmosphere are in any sense cool. In fact, we find from the position of the dark lines of the solar spectrum, that the vapours of magnesium and sodium, of iron, copper, and other metals, exist in the true solar atmosphere, which