In Plate [6] I have given a series of views of Mars much more distinct than an observer may expect to obtain with moderate powers. I add a chart of Mars, a miniature of one I have prepared from a charming series of tracings supplied me by Mr. Dawes. The views taken by this celebrated observer in 1852, 1856, 1860, 1862, and 1864, are far better than any others I have seen. The views by Beer and Mädler are good, as are some of Secchi's (though they appear badly drawn), Nasmyth's and Phillips'; Delarue's two views are also admirable; and Lockyer has given a better set of views than any of the others. But there is an amount of detail in Mr. Dawes' views which renders them superior to any yet taken. I must confess I failed at a first view to see the full value of Mr. Dawes' tracings. Faint marks appeared, which I supposed to be merely intended to represent shadings scarcely seen. A more careful study shewed me that every mark is to be taken as the representative of what Mr. Dawes actually saw. The consistency of the views is perfectly wonderful, when compared with the vagueness and inconsistency observable in nearly all other views. And this consistency is not shown by mere resemblance, which might have been an effect rather of memory (unconsciously exerted) than observation. The same feature changes so much in figure, as it appears on different parts of the disc, that it was sometimes only on a careful projection of different views that I could determine what certain features near the limb represented. But when this had been done, and the distortion through the effect of foreshortening corrected, the feature was found to be as true in shape as if it had been seen in the centre of the planet's disc.
In examining Mr. Dawes' drawings it was necessary that the position of Mars' axis should be known. The data for determining this were taken from Dr. Oudemann's determinations given in a valuable paper on Mars issued from Mr. Bishop's observatory. But instead of calculating Mars' presentation by the formulæ there given, I found it convenient rather to make use of geometrical constructions applied to my 'Charts of the Terrestrial Planets.' Taking Mädler's start-point for Martial longitudes, that is the longitude-line passing near Dawes' forked bay, I found that my results agreed pretty fairly with those in Prof. Phillips' map, so far as the latter went; but there are many details in my charts not found in Prof. Phillips' nor in Mädler's earlier charts.
I have applied to the different features the names of those observers who have studied the physical peculiarities presented by Mars. Mr. Dawes' name naturally occurs more frequently than others. Indeed, if I had followed the rule of giving to each feature the name of its discoverer, Mr. Dawes' name would have occurred much more frequently than it actually does.
On account of the eccentricity of his orbit, Mars is seen much better in some oppositions than in others. When best seen the southern hemisphere is brought more into view than the northern because the summer of his northern hemisphere occurs when he is nearly in aphelion (as is the case with the Earth by the way).
The relative dimensions and presentation of Mars, as seen in opposition in perihelion, and in opposition in aphelion, are shown in the two rows of figures.
In and near quadrature Mars is perceptibly gibbous. He is seen thus about two months before or after opposition. In the former case, he rises late and comes to the meridian six hours or so after midnight. In the latter case, he is well seen in the evening, coming to the meridian at six. His appearance and relative dimensions as he passes from opposition to quadrature are shown in the last three figures of the upper row.
Mars' polar caps may be seen with very moderate powers.
I add four sets of meridians (Plate [6]), by filling in which from the charts the observer may obtain any number of views of the planet as it appears at different times.
Passing over the asteroids, which are not very interesting objects to the amateur telescopist, we come to Jupiter, the giant of the solar system, surpassing our Earth more than 1400 times in volume, and overweighing all the planets taken together twice over.
Jupiter is one of the easiest of all objects of telescopic observation. No one can mistake this orb when it shines on a dark sky, and only Venus can be mistaken for it when seen as a morning or evening star. Sometimes both are seen together on the twilight sky, and then Venus is generally the brighter. Seen, however, at her brightest and at her greatest elongation from the sun, her splendour scarcely exceeds that with which Jupiter shines when high above the southern horizon at midnight.