694 



THE POPULAR SCIENCE MONTHLY. 



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 varia- 

 tion 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 dis- 

 tance, can not vary. The eccentricity is in- 

 creased or diminished by diminishing or in- 

 creasing the minor axis, the major axis re- 

 maining 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 av- 

 eraging, 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 densi- 

 ty 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 hemi- 

 sphere, 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 hemi- 

 sphere 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 boun- 



daries 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 over- 

 flowed 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 pres- 

 ent. But both Mr. Croll and Mr. Merriman, 

 from whom Mr. Norton is accused of pla- 

 giaiizing, 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 reuslt 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 

 M. Lyford. 

 Watekville, Maine, Jamiary 26, 1880. 



ARSENIC IN KINDERGARTENS. 



Messrs. Editors. 



There has been of late, in the local news- 

 papers, a good deal of discussion, pro and 

 tow, concerning the merits and demerits of 

 the Kindergarten system. Without presum- 

 ing 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, tlie aim of such amuse- 

 ments 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 linow 

 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 de- 

 rived 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 recog- 



