The maps included in this work have been photographed from a globe ofMars specially made for the purpose from various charts. In all the mapsthe south is at the top and the north at the bottom; and the seriesshows the general surface configuration all round the planet, togetherwith the principal canal lines which have been observed; but many othercanal lines exist, especially on the dark areas near the south pole.These lines are usually straight and uniform in width throughout theirwhole length: indeed it is difficult to mark them upon a globe so thatthey shall appear as regular and uniform as they are actually seen onthe planet.
The names on the maps are those now generally accepted and used byastronomers.
The "Greenwich" of Mars, _i.e._ the point on the Meridian from whichastronomers reckon the Martian longitudes, is indicated by the apex ofthe small triangular light area just above the equator in Map I. It ismarked on the map as "Fastigium Aryn," and is chosen as longitude "0,"because from its general outline it cannot be mistaken by observers.
"Sirapion," the supposed landing-place of the travellers mentioned inthe story, is shown on Map III., just above the central and lowest pointof the dark area at the top of the map. This name will not be found uponany other map of Mars.
The chart showing the relative positions of the Earth and Mars duringthe years 1909-10 is reduced and modified from one prepared accuratelyto scale by the author for his own use in connection with the book. Fromit the reader will gain a clear idea of the shape of the two orbits andhow they are placed with regard to each other.
It also shows the course supposed to be taken by the air-ship on itsoutward and homeward journeys, and the point reached when one of thetravellers desired to turn back; together with the alternative routeswhich were then discussed.
This chart, and the other one showing the positions of the two planetsat different oppositions of Mars, will enable the reader to understandhow it is that Mars approaches so much nearer to the earth at someoppositions than it does at others. The positions of the oppositionsfrom 1916 to 1922 are only approximations, as no exact data are yetavailable. The earth is closest to the orbit of Mars about the 27th ofAugust each year, and if Mars comes into opposition about that date itis then only about thirty-five million miles away. If, however, theopposition occurs near the 22nd February, the earth is then at itsgreatest possible distance from the orbit of Mars, and that planet willthen be over sixty million miles away: appearing very much smaller thanwhen at its most favourable point of approach.
On the 18th of September, 1909, Mars was only slightly over thirty-sixmillion miles from the earth, and it will be fifteen years before such afavourable situation again occurs.
The nearest point of approach does not necessarily occur on the actualdate of the opposition. In 1907 Mars was in perigee, as it is termed,seven days after the opposition; while in 1909, perigee was beforeopposition.
The diagram showing the positions and movements of the planets duringthe period covered by the outward voyage of the _Areonal_ issufficiently explained by the notes printed thereon. It may, however, bepointed out that though the orbits of the planets are all elliptical,especially those of Mercury and Mars, they are so nearly true circlesthat, when reduced to the scale of these diagrams, they practicallybecome circles. The exaggerated ellipses so often found in astronomicalbooks are very misleading. The orbits of Mercury and Mars have anappearance of ellipticity because the sun does not occupy the centralpoint in the diagram.
The view of the moon is photographed from a large coloured drawing bythe author, which occupied many months in preparation and execution. Itshows all the principal formations seen through the telescope as themoon passes through its various phases, but it must be understood thatthe formations can never all be seen at one view as shown in thispicture. As the sun rises on any particular formation the details aregradually revealed by the long shadows cast by the more elevatedportions when the sun is low down in the lunar sky. As the sun riseshigher and higher the shadows grow shorter and shorter, and when the sunis vertically over the formation the shadows entirely disappear; alldetails are thus rendered invisible.
When the moon is full the sun is practically vertical over the wholelunar surface, so the only details then seen are those which are vaguelybrought out by differences in tint.
The bright ray-streaks are only suggested in the picture, because, ifshown complete, they would have the same effect as upon the moon, viz.they would entirely obliterate all the formations over which theypassed.
The Key Map indicates the principal lunar formations, and includes thenames of those mentioned in the book.
The last two plates in the book are from drawings made at the telescope(a 12-inch Calver reflector) by the Rev. T. E. R. Phillips. Theopposition of 1909 was not favourable for the observation of Martiandetails from England; for although the planet was near to us, it was toolow down in the sky; and many of the nights were either cloudy ormisty.