Page:Popular Science Monthly Volume 16.djvu/724

 vernal to the autumnal equinox as from the autumnal to the vernal, whatever may be the position of the apsides, and whatever the eccentricity of the orbit.

2. In speaking of the variation in the eccentricity, the author says: "There is one more factor in this problem which must be considered, and that is the periodical variation in the eccentricity of the earth's orbit. Sometimes the line of the apsides is longer than at other times."

I am at a loss to account for this last statement. The author must have known that the mean distance of a planet from the sun is one of the two invariable elements of the planetary orbits. Of course the line of the apsides, which is the major axis of the orbit, and therefore twice the mean distance, can not vary. The eccentricity is increased or diminished by diminishing or increasing the minor axis, the major axis remaining always the same.

3. In discussing the displacement of the earth's center of gravity by an accumulation of ice at the pole, it is said, "Now push the center of gravity 2,000 feet toward the north, and the Arctic Ocean would be so much deeper over the pole, and the water would be about 1,000 feet deeper at the latitude of 45°. To accomplish this result, we must calculate that the space within the Arctic Circle was covered by an ice-cap averaging, perhaps, 8,000 feet in thickness—an entirely supposable case."

By calculation, I find that, if all the water to form this ice-cap were taken from within the Antarctic Circle, and if the density of ice were equal to that of the earth, the above statement would be approximately correct; but, allowing for the difference of density, the cap must be more than eight miles in thickness; and, if the water to form the cap were taken equally from all parts of the earth's surface, the thickness must be more than sixteen miles.

Perhaps it should be said, however, that, according to Mr. Croll, no such amount of displacement is required. He estimates that the transfer of an ice-cap two miles thick from the southern to the northern hemisphere, which would displace the center of gravity about 380 feet, would satisfy all the demands of the glacial phenomena.

4. But, if Mr. Norton's article should be received as an exponent of the present views of those who advocate this theory, it would be most seriously misleading in the date to which it refers the age of ice. It is said: "Unless astronomical calculations fail, the last great summer of the northern hemisphere commenced some 6,500 years ago. When it began, northern America, Europe, and Asia were frozen and deluged. The Arctic Ocean extended to a line south of the present bed of the Great Lakes. The Alps and the Altai were also southern boundaries of this ocean. Europe was the home of a swarthy, dwarfish race, who hunted the aurochs and great hairy mastodon at the foot of the glaciers that then half overflowed the continent."

Thus the age of ice is referred to the last mild aphelion winter, when the earth's orbit was but slightly more eccentric than at present. But both Mr. Croll and Mr. Merriman, from whom Mr. Norton is accused of plagiarizing, refer the glacial epoch to a period of great eccentricity, from 80,000 to 240,000 years ago.

Indeed, the warmest advocates of the great year theory freely admit that, with the eccentricity no greater than it has been at any time within the last 80,000 years, the age of ice could not have been the reusltresult [sic] of such a cause. It scarcely need be added that some refer the ice age to a period of still greater eccentricity, some 800,000 years ago

Messrs. Editors.

has been of late, in the local newspapers, a good deal of discussion, pro and con, concerning the merits and demerits of the Kindergarten system. Without presuming to decide whether the system is good or bad, I wish to bring under the notice of your readers a simple fact in connection with it that is of more than local interest. A friend of mine in Pittsburg, who has a little daughter being instructed (or amused) in one of the Kindergartens here, recently handed me some pieces of a green-colored paper which the child brought home from the institution, and told me that one of the amusements of children in such institutions was to cut figures out of various colored papers and fashion them into designs of different kinds, the aim of such amusements being to instruct in distinguishing various shades of color and differences of form. The green paper above mentioned I have very carefully examined, and I find that it contains an abundance of arsenite of copper, which most people nowadays 'know to be poisonous. In these days of reckless assertion by pretended men of science, it may be well to fortify my statement, and I accordingly send you two hermetically sealed tubes, one of which contains a mirror of metallic arsenic, and the other a ring of crystals of arsenious acid, both of them derived from the green paper, of which I also send you a sample. Several mirrors were obtained from a fragment of paper half the size of the piece inclosed, and material enough was procured from it to produce several more. The crystals can be