The spectroscope and the camera are now the chief engines of solar research. Mere telescopic observation, though always an indispensable adjunct, may be considered to have sunk into a secondary position. But the spectroscope and the camera, still more than the telescope, lie at the mercy of atmospheric vapors and undulations. The late Professor Henry Draper, of New York, an adept in the art of celestial photography, stated in 1877 that two years, during which he had photographed the moon at his observatory on the Hudson on every moonlit night, yielded _only three_ when the air was still enough to give good results, nor even then without some unsteadiness; and Bond, of Cambridge (U. S.) informed him that he had watched in vain, through no less than seventeen years for a faultless condition of our troublesome environing medium.[13] Tranquillity is the first requisite for a successful astronomical photograph. The hour generally chosen for employing the sun as his own limner is, for this reason, in the early morning, before the newly emerged beams have had time to set the air in commotion, and so blur the marvellous details of his surface-structure. By this means a better definition is secured but at the expense of transparency. Both are, at the sea-level, hardly ever combined. A certain amount of haziness is the price usually paid for exceptional stillness, so that it not unfrequently happens that astronomers see best in a fog, as on the night of November 15th, 1850, when the elder Bond discovered the “dusky ring” of Saturn, although at the time no star below the fourth magnitude could be made out with the naked eye. Now on well-chosen mountain stations, a union of these unhappy divorced conditions is at certain times to be met with, opportunities being thus afforded with tolerable certainty and no great rarity, which an astronomer on the plains might think himself fortunate in securing once or twice in a lifetime.