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Friday, March 4th, 1904. Mr. P. E. Vizard, F.R.A.S., Vice- 
President in the chair. 
Professor W. R. Cassie, M.A., gave a lecture on ‘‘ The Planet 
Mars ”’ illustrated with lantern slides. Professor Cassie described 
the position of Mars in the solar system and its relative size to 
other bodies, its diameter being about half that of the earth. 
Its motion relative to the earth in a series of loops was clearly shown 
by means of a diagram in the form of a curve, the earth being 
supposed to be fixed at the centre. The most favourable times 
for observation are those in which Mars is in opposition, which occur 
every two years. The planet is then nearest to us and presents 
a fully illuminated disc, though there is a great advantage in 
some oppositions in this respect over others, these occurring every 
fifteen years. The lecturer showed drawings of the planet made 
by Sir William Herschel at the end of the eighteenth century, in 
which the polar caps of supposed snow were seen. Herschel deter- 
mined the day of Mars to be of about twenty-four hours’ duration, 
and showed that in the obliquity of its equator it also resembles 
our earth. Lowell has made careful observations of Mars at his 
observatory at Flagstaff, Arizona, a site selected for the clearness of 
-its atmosphere. The surface of the planet is of a reddish colour 
with patches of green, which have been described as seas, though 
it has been shown that, since the light reflected from them is not 
polarized, they do not contain water. Lowell observed that, as 
the polar caps diminished in the planet’s Spring, patches of white 
were left upon spots which, by their projection beyond the planet’s 
limb during rotation, he determined to be mountains. From these 
patches, at times, he observed brilliant flashes of light, which 
_ failed in a few minutes as the planet rotated. These flashes he 
_ found were polarized, and concluded that they were reflected from 
_ the icy slopes of these mountains, as one may often observe the 
> sunlight to be reflected temporarily from a distant window. 
Schiaparelli of Milan first observed, in 1877, certain lines on the 
surface of Mars, which he called ‘‘ Canali.” He paid great attention - — 
to them for some years, discovering more of them and many which 
appeared double. Until 1886 no one else had succeeded in seeing - 
_ them; but from this date the number of these canals was greatly 
' increased by different observers. They are drawn as straight 
_ lines across the “seas.” Where they cross a small expansion is_ 
' generally observed. Lowell’s observations led him to believe that 
_ the darkening seas round the polar cap-in the Spring consist of 
_ water from the melting snow; that this water finds its way over 
_ the planet’s surface by means of these “ canals,” whose function 
_ is that of irrigation ; that with the extending of the water a green 
_ tint spreads along the neighbourhood of the canals, which he 
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