Observations made by Boussingault at Quito in 1831, compared with those from 1878 to 1881, showed a decrease from 15.2° Centigrade to 13.27° Centigrade.
Records made by Hall from 1825 to 1827 give averages of 16.1° Centigrade, 15.52° Centigrade, and 15.6° Centigrade. This decrease holds good for all points in the inter-Andean region where records have been kept.
Yet we know that the falling temperature in the northern temperate latitudes is not brought about by a yearly increase of cold, because, when the arctic channels are somewhat obstructed with icebergs, the movement of arctic waters through them is lessened; and, therefore, during such times the Gulf Stream, meeting with less opposition from arctic currents while flowing northward, is able to move a larger volume of its waters into the arctic seas, thus warming their waters sufficiently in a few seasons to clear the obstructed channels, and also somewhat soften for several successive years the temperature of such lands as border on the seas of that region.
And in this way we account for the mild seasons which at times follow those of lower temperature in high northern latitudes.
But, when the detained icebergs are set adrift, and currented into the temperate North Atlantic, the heat consumed while melting such numerous bodies of ice is able to more than overcome the warmth gained during the temporary detention of ice in the northern seas. Thus, under such considerations, it appears that the conditions are favorable for the growth of glaciers in the high northern latitudes.
I have pointed out the manner in which the superior oceans in the southern hemisphere are obtaining a lower temperature, and how they impart their coldness to the tropical currents, and in this way slowly cool the waters of all oceans. Thus it appears that the northern temperate zone, with all other parts of the earth, is slowly approaching a cold epoch.
Several writers on climatic changes have expressed their views as to the number of glacial and mild periods that have been perfected since the conditions have been favorable for their appearance on the globe. According to my views, while considering the reasons for the occurrence of the great glacial periods which have left such extensive traces on the land, it seems certain that two very cold epochs have possessed the earth, separated by a warm period; and, possibly, other preceding cold epochs of less intensity have possessed the high latitudes, with intervening periods of mildness. But the earlier cold periods, if they ever existed, were comparatively short, because the Cape Horn channel during such times possessed less capacity than in the later periods, and, therefore, was more easily and quickly obstructed by the natural methods previously explained.
Consequently, the independent circulation of the southern ocean was sooner arrested than during the later epoch, when the channel had become enlarged by erosion from heavy glaciers and icebergs; and meanwhile the same conditions may have governed the arctic channels which give an independent circulation to the arctic waters which surround Greenland, and thus, in connection with cold epochs in the southern hemisphere, have caused periods of cold of small intensity to occur in the high northern latitudes, and it may happen in the future that more ice periods will be perfected than the one now progressing.
Still, it is well to bear in mind that the Cape Horn channel, which is the real cause of glacial periods having occurred in both the northern and southern hemispheres, in the manner previously explained, is being made wider and deeper during each succeeding ice age. For this reason the latest cold epoch will require a longer continuance of cold to obstruct the channel than the cold period preceding. Therefore, it appears that the time will come when there will be such great accumulations of ice stored on the land and in the sea before the enlarged Cape Horn channel can be closed that, when it is closed, there will not be sufficient warmth remaining in the tropical seas to unite with the sun’s rays to subdue the intense cold stored in the immense gatherings of ice. And thus the earth, which began its career with a warm temperature, and so continued for long ages, will finally terminate in an endless glacial age.
The statements made by General Cowell in Science of Nov. 25, 1892, in reference to the alleged discovery of the second rotation of the earth by Major-general Drayson, represents the discovery as affording a new solution for the cause or causes of an ice age.