photographs showing the Martian canal lines were projected on to the
screen by a lantern, and thus their convincing evidence was clearly
brought before the whole of that vast audience.

Another very interesting series of photographs showed the coming and
going of the first frost of the season in the antarctic regions of Mars.
This frost was first observed and photographed at Flagstaff on the 16th
November, 1909, and other photographs were taken on the 22nd of that
month.

In connection with these, Professor Lowell quaintly remarked that, "To
chronicle thus the very weather on our neighbour will convince any one
that interplanetary communication has already commenced; and that, too,
after the usual conventional manner by mundane greetings."

Referring to the photographs, it was pointed out that the human eye can
see at least ten times as much as a photograph can show as regards
planetary detail. This, though not generally known, is perfectly true,
and it may be explained thus: We know that in terrestrial photography
the camera will reveal many details which the eye is apt to overlook;
and, by very long exposures, even celestial photography will give a
similar result. In _planetary_ photography, however, exposures must be
very short, and the picture obtained is so very tiny that it cannot show
all that the eye could see. Under good conditions, therefore, the eye at
the telescope will always see immensely more of the finer details on a
planet than any camera could show.

The great value of the photographs of Mars lies in the fact that they
demonstrate beyond the possibility of doubt the existence of certain
fine markings which many observers have seen and drawn, but as to the
reality of which others, less skilled or less favourably situated, have
been extremely sceptical. If the fine lines had no existence on the
planet they could not be photographed.

In drawing attention to the details on these photographs Professor
Lowell emphatically declared that, "The lines you see are
'_certainties_,' not matters admitting of the slightest question, for
all their strange regularity. Not only I, but all my assistants, have
seen them thousands of times the same, and sometimes with all the
clearness and sharpness of etchings or steel engravings.

"An optical mistake," he then remarked, "which has latterly been hailed
as showing that the lines were not lines but a series of dots, was made
the other day in France. The observer saw