For, having found out by a careful series of observations, the parts of Mars' orbit where the planet entered upon its various seasons, he [William Herschel] noted that, soon after mid-winter of the northern hemisphere, the northern white spot attained its greatest dimensions, while the southern was reduced to a tiny oval of light; whereas half a Martial year later, the southern spot was at its largest, and the northern a mere speck when compared with its winter appearance.