vatory was built at
Flagstaff, Arizona, far away from towns and smoke, at an altitude of
over 6000 feet above the sea-level, the site being specially selected on
account of the clearness and purity of its atmosphere; while the
observatory, being high up above the denser and more disturbed strata of
air, afforded the most favourable situation possible for the proper
observation of delicate planetary detail.

"There he continued the work which Schiaparelli had commenced, and,
together with the colleagues with whom he has been associated, has, by
long-continued and most systematic work, added greatly to our knowledge
of Mars. Year after year has seen the addition of more lines on our maps
of the planet, whilst many interesting discoveries have been made--one
being that some of the fine lines were double, the second line always
being equidistant from the first one throughout its whole length, no
matter whether the lines were straight or curved.

"This caused a further outcry of objection. The observers were told that
they had been overstraining their eyesight so that they 'saw double,'
and also that they had been using telescopes not properly focussed. Such
objections seem almost beyond argument, for no practical observer could
use an improperly focussed instrument without at once discovering the
defect.

"Besides, if the double lines were the result of eye-strain, or any
other defect which might cause such illusions, all the lines would have
been seen double, or at least all the lines running at the same angles;
but as a matter of fact only a very small proportion of the lines were
so seen, and it made no difference what position they occupied on the
disc, or at what angles they were presented. Some of the doubles were,
in fact, curved lines; and another point was that in some cases they
were only doubled at certain seasons of the year.

"Other observers who saw the lines were charged with having studied the
maps of Schiaparelli and Lowell until they had become obsessed with the
lines, and when they looked through the telescope simply fancied they
saw them!

"In England our atmospheric conditions are seldom really favourable to
the proper seeing of the finer detail, and the very faint lines cannot
be seen at all. The lines that are visible do not appear thin and sharp
as they do to observers in more favoured climes, but rather as diffused
smudgy lines, and so they are drawn by the observers. On a few
occasions of exc