The remarkable successes of astronomical photography, which depended
upon the plate's power of accumulation of a very feeble light acting
continuously through an exposure of several hours, were worthy to be
regarded as a new revelation. The first chapter opened when, in 1880,
Dr. Henry Draper obtained a picture of the nebula of Orion; but a more
important advance was made in 1883, when Dr. Common, by his
photographs, brought to our knowledge details and extensions of this
nebula hitherto unknown. A further disclosure took place in 1885, when
the Brothers Henry showed for the first time in great detail the
spiral nebulosity issuing from the bright star Maia of the Pleiades,
and shortly afterward nebulous streams about the other stars of this
group. In 1886 Mr. Roberts, by means of a photograph to which three
hours' exposure had been given, showed the whole background of this
group to be nebulous.
In the following year Mr. Roberts more than doubled for us the great
extension of the nebular region which surrounds the trapezium in the
constellation of Orion. By his photographs of the great nebula in
Andromeda, he had shown the true significance of the dark canals which
had been seen by the eye. They were in reality spaces between
successive rings of bright matter, which appeared nearly straight,
owing to the inclination in which they lay relatively to us. These
bright rings surrounded an undefined central luminous mass. Recent
photographs by Mr. Russell showed that the great rift in the Milky Way
in Argus, which to the eye was void of stars, was in reality uniformly
covered with them.