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CORRESPONDENCE.

CORRESPONDENCE.
 

CLOSE OF THE GLACIAL PERIOD.

Editor Popular Science Monthly:

Geologists who are only slightly versed in astronomy are apt to make a serious mistake on this subject. The latest which has fallen under my notice is by Prestwich. in the article entitled The Position of Geology, in the February number of this periodical, page 541._ He says: "The last of these astronomical periods was calculated to have commenced two hundred and fifty thousand years and to have ended eighty thousand years ago. These numbers have become stereotyped as those of the beginning and the end of the Glacial period."

A slight acquaintance with this subject ought to prevent mistakes such as the above. They are stereotyped only to those who give little or no heed to the actual dates and as little to a universal law of Nature touching the cumulative effects of constantly acting forces. These effects were clearly set forth by Prof. Le Conte some years ago in treating of this general subject. The day of the summer solstice is not the day of greatest heat or the middle of the hot season; nor is the day of the winter solstice in the middle of the cold season. The maximum in the two cases occurs about six weeks after those dates respectively, an amount about equal to one fourth of the whole time from one extreme to the other. These are elementary truths, and whoever omits them in this discussion repeats the old story of "playing Hamlet with Hamlet left out."

The following is a brief statement of the essential points in the case: Two hundred and fifty thousand years ago[1] the eccentricity of the earth's orbit was very nearly what it is now, and consequently the climate of these two distant periods, so far as it may depend on the eccentricity, was not very different. The eccentricity had been less, but was then increasing, and had so been for ten thousand years. It continued to increase for about fifty thousand years longer, becoming then nearly three times its present value. Then for another like period it diminished till it became about once and a half its present value. Then again for a second time it increased for about fifty thousand years, becoming about two and a half times the original value. This was one hundred thousand years ago. The decline again commenced, and eighty thousand years ago the eccentricity was more than double its present value. It is therefore evident is plain as an axiom—that the Glacial period did not end then and there. The eccentricity continued to be greater than it is now for twenty thousand years more. And for this long period of one hundred and ninety thousand years the eccentricity, on the average, was more than twice what it is now. Those who disregard these facts have not fully grasped the question. It would better accord with truth to say that sixty thousand years ago the Glacial period was making ready "to go out of business."

If we allow only thirty thousand years for the undoing of the effects of the one hundred and ninety thousand—and the allowance is certainly moderate—the close of the Glacial period was only thirty thousand years ago, and that date is comparatively recent when counting geological time. It appears, then, that there is no irreconcilable difference between those geologists who reject Croll's theory by reason of the alleged remoteness of the Glacial period and those who think there "may be something" in that theory. And the more especially is this the case since the recent discovery of the old outlet of the upper lakes through Lake Nipissing and the Ottawa River and the relatively late period when the waters of all the upper lakes began to flow to the sea by way of the Niagara.R. W. McFarland.

Columbus, Ohio, February, 1894.

 

 

DOG PSYCHOLOGY.

Editor Popular Science Monthly;

Dear Sir: I was greatly interested in Mr. Monteith's article on "The Psychology of the Dog," in the February number, and desire to supplement his paper with some observations of a dog of my own. The animal was a pug—not full-blooded, but with a cross of some other kind; yet he had all the characteristic markings of that breed, and his general appearance was the same, except that his nose was a trifle longer and not so stubby.

"Gyp" was intelligent to a remarkable degree, and from some of his actions I firmly believe that he not only understood what was said to him, but he was capable also of continuous thought, and could reach conclusions. That he understood many words, and could distinguish between them, I am satisfied.

His mistress taught him that when some candy was placed before him, of which he was very fond, if she said, "That's Democrat," he must not touch it, but when the word "Republican" was uttered he at once ate it.

When "Gyp" was thirsty he would go into the kitchen and sit patiently at the sink waiting for a drink; but if, after waiting for


  1. See American Journal of Science, August, 1880.