THE PLANET MARS IN FEBRUARY 18C9. 
45 
parallels properly presented (on the scale — in each case — of the 
corresponding drawing by Mr. Dawes). Then beginning with 
the most promising view I placed the tracing-paper over the 
picture of the planet, giving that position to the polar axis which 
corresponded most closely with the assigned position of the polar 
snow-caps. Then on a projection of the meridians and parallels 
of a globe on the equidistant projection, I drew in the lands and 
seas of Mars as they appeared under the meridian-lines on the 
tracing-paper. I next repeated the process for other drawings 
in which the same features were presented. 
At first there was. little accordance between the results thus 
pencilled on my chart-projection. This was caused by erroneous 
selections of the axial line of Mars, which — it must be remem- 
bered — does not correspond with the position of the polar snow- 
caps. But gradually I began to get over this difficulty and 
the views began to show a much closer agreement. Still there 
were slight discrepancies, and these, when reduced as much as 
possible by shifting the assumed position of the axis, I was 
obliged to ascribe to such slight errors as could not fail to appear 
in drawings so full of detail and taken under such circumstances 
of difficulty as were Mr. Dawes’ pictures. Therefore, having 
drawn in all the outlines deducible from pictures nearly ap- 
proaching each other in phase, I took a mean outline through 
the others to be as nearly as possible correct. 
It must be understood that the amount of Mars’ surface 
covered by one such series of processes would be very much less 
than a full hemisphere, since — firstly, the part of Mars near the 
limb was not drawn in so distinctly in Dawes’ pictures as the 
rest, and secondly, a small mis-drawing in an orthographic pre- 
sentation of a planet becomes much more important as we leave 
the centre of the disc, so that I did not consider myself justified 
in using those delineations which were not near the centre. It 
must also be remembered that as the drawings were not taken 
at periods separated by regular intervals of Martial time, it was 
very necessary to apply to each a correction calculated according 
to the true value of Mars’ rotation-period. Thus it will be 
understood that before the whole of the surface of Mars had 
been charted a considerable amount of labour had been given 
to the subject. Those who have never tried work of this sort 
would hardly be able to conceive how perplexing it often be- 
comes. But one circumstance was very pleasing. I found that 
the more carefully I worked at the chart, the more thoroughly 
the true value of Mr. Dawes’ drawinofs came out. I had 
had little conception, when I began the work, either of the 
acuteness of his vision or of the accuracy of his powers of deline- 
ation. The tracings he sent me were partially covered with 
faintly marked streaks which I had at first supposed to be 
