to be white, which alternated with bands of corresponding width from which the sulphur was absent. As one looks down on the bottle from above these rings are arranged symmetrically with regard to a median line analogous to the black band in the optical figure but the two axial centers are not placed in the line at right angles to this plane, but the two systems of rings sag symmetrically below this line. It is clear that this bottle was made by the old fashioned method of blowing, that the median plane separating the two systems of rings was the plane of junction of the halves of the wooden mould in which the clot of glass was blown to the shape of the bottle and that the glass chilled quickest along this line and became most viscid. The continued blowing then caused the glass to flow symmetrically in the two segments thus marked out by the lines of flow shown in the figure. The flow was not directly outward but outward and downward, giving the sag in the figure described above, because the mould was placed on one side during the blowing or because one side of the mould was more open than the other. As the glass flowed outwardly a rythmical difference of surface texture developed and the bands of rougher and smoother surface were drawn out into symmetrical rings. This difference of surface was brought out by the sulphur which was able to crystallize on only one of the surfaces, probably on the rougher one, in which the escape of heat or electricity from the irregularities may have favored crystallization. It is an illustration of what occurs so frequently in crystals, that faces of a given form will be incrusted and those of another avoided by the crystallization of a foreign body. 2. A remarkable Geode. Figure 2. Many years ago a missionary graduate sent to the geological museum of Amberst College, a great geode from the Orange river in South Africa, which is remarkable for its great size, the deep regular pittings like the eyes of a potato and rich translucent amber color and firm polish of its surface. It was 14 inches long and 10 inches high and 91⁄2 thick. I had many times taken a hammer with the intention of learning what was in the interior but desisted-the form was so perfect. |