The small apparent size of the planet explains how it was that Galileo does not seem to have been able to detect any markings upon it. In 1659, Huyghens laid the foundation stone of areography by observing some dark spots, and determining from their apparent movements that the planet had a rotation on its axis, which it accomplished in about the same time as the Earth. Small and rough as are the drawings that Huyghens made, the identification of one or two of his spots is unmistakable. Seven years later, in 1666, both Cassini and Hooke made a number of sketches, and those by Hooke have been repeatedly used in modern determinations of the rotation period of the planet. The next great advance was made by Sir William Herschel, who, during the oppositions of 1777, 1779, 1781, and 1783, determined the inclination of the axis of Mars to the plane of its orbit, measured its polar and equatorial diameters, and ascertained the amount of the polar flattening. He paid also special attention to two bright white spots upon the planet, and he showed that these formed round the planet's poles and increased in size as the winter of each several hemisphere drew on and diminished again with the advance of summer, behaving therefore as do the snow caps of our own polar regions.
The next stage in the development of our knowledge of Mars must be ascribed to the two German astronomers, Beer and Mädler, who made a series of drawings in the years 1830, 1832 and 1837, by means of a telescope of 4 inches aperture, from which they were able to construct a chart of the entire globe. This chart may be considered classic, for the features which it represents have been observed afresh at each succeeding opposition. Mars, therefore, possesses a permanent topography, and some of the markings in question can be identified, not only in the rough sketches made by Sir William Herschel, but even in those made by Hooke and Cassini as far back as the year 1666. In the forty years that followed, the planet was studied by many of the most skilled observers, particularly by Mr. J. N. Lockyer in 1862, and the Rev. W. R. Dawes in 1864. In 1877, the late Mr. N. E. Green, drawing-master to Queen Victoria, and a distinguished painter in water colours, made a series of sketches of the planet from a station in the island of Madeira 2000 feet above sea-level. When the opposition was over, Mr. Green collected together a large number of drawings, and formed a chart of the planet, much richer in detail than any that had preceded it, and from his skill, experience and training as an artist he reproduced the appearance of the planet with a fidelity that had never been equalled before and has never been surpassed since. At this time it was generally assumed that Mars was a miniature of our own world. The brighter districts of its surface were supposed to be continents, the darker, seas. As Sir William Herschel had already pointed out long before, the little world evidently had its seasons, its axis being inclined to the plane of its orbit at much the same angle as is the case with the Earth; it had its polar caps, presumably of ice and snow; its day was but very little longer than that of the Earth; and the only important difference seemed to be that it had a longer year, and was a little further off the Sun. But the general conclusion was that it was so like the Earth in its conditions that we had practically found out all that there was to know; all that seemed to be reserved for future research was that a few minor details of the surface might be filled in as the power of our telescopes was increased.