tant telescopic observation upon the planet. On November 28, 1659, at 7 p.m., he made the first drawing of the planet worthy the name, for on it is the first identifiable feature ever made out by man on the surface of Mars. This feature is the Hourglass Sea, now more commonly known as the Syrtis Major. The accompanying cut of it is reproduced from Flammarion. If the dark patch in it be compared with the markings in time other pictures of the planet, shown later in this book, it will be seen that the patch can be none other than the Hourglass Sea.
_-_Huyghens%27_drawing_of_the_Syrtis_Major,_Nov._28,_1659.jpg)
Now, innocent as it looks of much detail, Huyghens’ drawing is perhaps the most important one of Mars that has ever been made. For, from his observations of the spot it depicts at successive dates, he was able to prove that Mars rotated on his own axis, and to determine the time of that rotation, about 24 hours. As he subsequently came to doubt his results, the honor of the discovery rests with Cassini, who, in 1666, definitely determined that the planet rotated in 24 hours 40 minutes. Thus was it
