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
besides the 'seas' of various sizes there were numerous very small black
spots apparently quite circular and occurring at every intersection or
starting-point of the 'canals.' Many of these had been seen by
Schiaparelli as larger and ill-defined dark patches, and were termed
seas or lakes; but Mr. Pickering's observatory was at Arequipa in Peru,
about 8000 feet above the sea, and with such perfect atmospheric
conditions as were, in his opinion, equal to a doubling of telescopic
aperture. They were soon detected by other observers, especially by Mr.
Lowell in 1894, who thus wrote of them:

"Scattered over the orange-ochre groundwork of the continental regions
of the planet, are any number of dark round spots. How many there may be
it is not possible to state, as the better the seeing, the more of them
there seem to be. In spite, however, of their great number, there is no
instance of one unconnected with a canal. What is more, there is
apparently none that does not lie at the junction of several canals.
Reversely, all the junctions appear to be provided with spots. Plotted
upon a globe they and their connecting canals make a most curious
network over all the orange-ochre equatorial parts of the planet, a mass
of lines and knots, the one marking being as omnipresent as the other."

_Changes of Colour recognised._

During the oppositions of 1892 a