_Observed February_ 20, 1876. An observation of the cone of light whose axis lies along the Zodiac, whence it derives its name. It is drawn as seen in the west, with its base in the constellation Pisces, and its apex near the familiar group of the Pleiades in the constellation Taurus. The first bright star above the horizon in the base of the cone is the planet _Venus_ and at some distance above is the reddish disk of _Mars_, the two being in rare companionship as evening stars. Above the constellation Pisces, two bright stars of Aries lie just outside the cone at the right. The nearest bright star above these at the right is _Beta_, the leading star of the constellation Triangula. Further at the right the three prominent stars nearly in a line are, in ascending order, _Delta_, _Beta_ and _Gamma_ of the constellation Andromeda. Above these at the left, the brightest star of a quadrangular group of four is the remarkable variable star _Algol_ (_Beta_) of the constellation Perseus, which changes from the second to the fourth magnitude in a period of less than three days. At the left and a little above the Pleiades is the ruddy star _Aldebaran_, one of the Hyades and chief star in the constellation Taurus. These are the principal stars visible in this portion of the sky at the time of the observation. Their relative positions are represented as seen in the sky and not by the common method of star-atlases, which allows for the change from a spherical to a plane surface. Their magnitude in the order of brightness is indicated only approximately. PLATE VI.--MARE HUMORUM. _From a study made in 1875._