sen infers from lunar theory a reduced value for
the distance of the sun.
1854 Helmholtz's "gravitation theory" of solar energy.
1856 Piazzi Smyth's observations on the Peak of Teneriffe.
1857 Saturn's rings shown by Clerk Maxwell to be of meteoric
formation.
1857, April 27 Double-star photography initiated at Harvard College.
1858 Solar photography begun at Kew.
1858, Sept. 30 Perihelion of Donati's comet.
1859 Spectrum analysis established by Kirchhoff and Bunsen.
1859 Carrington's discovery of the compound nature of the
sun's rotation.
1859, Sept. 1 Luminous solar outburst and magnetic storm.
1859, Oct. 19 Merope nebula discovered by Tempel.
1859, Dec. 15 Chemical constitution of the sun described by Kirchhoff.
1860, Feb. 27 Discovery by Liais of a "double comet."
1860, May 21 New star in Scorpio detected by Auwers.
1860, July 18 Total solar eclipse observed in Spain. Prominences
shown by photography to be solar appendages.
1861, June 30 The earth involved in the tail of a great comet.
1861-1862 Kirchhoff's map of the solar spectrum.
1862 Solar hydrogen-absorption recognised by Angstrom.
1862, Jan. 31 Discovery by Alvan G. Clark of the companion of Sirius.
1862 Foucault determines the sun's distance by the velocity
of light.
1862 Opposition of Mars. Determination of solar parallax.
1862 Completion of _Bonner Durchmusterung_.
1863 Secchi's classification of stellar spectra.
1863 Foundation of the German Astronomical Society.
1864, March 5 Rotation period of Mars determined by Kaiser.
1864 Huggins's first results in stellar spectrum analysis.
1864, Aug. 5 Spectroscopic examination of Tempel's comet by
Donati shows it to be composed of glowing gas.
1864, Aug. 29 Discovery by Huggins of gaseous nebulae.
1864 Value of 91,000,000 miles adopted for the sun's
distance.
1864 Croll's explanation of glacial epochs.
1864, Nov. 23 Death of Struve.
1865, Jan. 4 Spectroscopic observation by Huggins of the occultation
of Eta Piscium.
1865, Jan. 16 Faye's theory of the so