_The Canals discovered by Schiaparelli._

Hence the great interest excited when Schiaparelli, at the Milan
Observatory, during the very favourable opposition of 1877 and 1879,
observed that the whole of the tropical and temperate regions from 60°
N. to 60° S. Lat. were covered with a remarkable network of broader
curved and narrower straight lines of a dark colour. At each successive
favourable opposition, these strange objects called _canali_ (channels)
by their discoverer, but rather misleadingly 'canals' in England and
America, were observed by means of all the great telescopes in the
world, and their reality and general features became well established.
In Schiaparelli's first map they were represented as being much broader
and less sharply defined than he himself and other observers found by
later and equally favourable observations that they really were.

_Discovery of the Double Canals._

In 1881 another strange feature was discovered by Schiaparelli, who
found that about twenty canals which had previously been seen single
were now distinctly double, that is, that they consisted of two parallel
lines, equally distinct and either very close together or a considerable
distance apart. This curious appearance was at first thought to be due
to some instrumental defect or optical illusion; but as it was soon
confirmed by other observers with the best instruments and in widely
different localities it became in time accepted as a real phenomenon of
the planet's surface.

_Round Spots discovered in_ 1892.

At the favourable opposition of 1892, Mr. W. H. Pickering noticed that