CHAPTER V THE DECADE 1860-1870. (By H. F. NEW ALL) A DECADE which was so full of activity and achievement in all branches of astronomical progress as that between 1860 and 1870, makes great demands on the self-restraint of an astronomer who is called upon to set forth the history of our Society at that time. There are great temptations to the historian to digress from the strict lines within which he should confine his efforts, and to allow himself to be guided in his refer- ences, not only to events in other decades, but also to researches which in truth belong to the history of Astronomy, and not to the history of the Society. This particular decade, 1860 to 1870, would certainly afford a very interesting chapter in the history of Astronomy. But that is not our present task ; still, some indication must be given of the activity of the decade with which we have to deal. In it we see the application of photographical methods to furnishing the best basis for lunar topography and to recording the complex phenomena of solar eclipses. We see the development of spectroscopy, not only as affording evidence of the widespread distribution of terrestrial chemical elements throughout the universe, but also as giving proof of the radical distinction between gaseous nebulae and unresolved star-clusters. We see the bold and pertinacious attack on the measurement of the line-of-sight velocities of stars by means of the spectro- scope. We see also another triumph of the spectroscope in the discovery of the nature of the solar prominences as outbursts of incandescent gas, and the almost simultaneous discovery of a method of daily observation of such prominences, which hitherto had been disclosed only during total eclipses of the sun. We see visual methods in the study of the positions and motions of sun-spots replaced by photographic records ; but not before the peculiarities of those motions and of the rotation of the sun had been demonstrated. 129 9
