Page:Popular Science Monthly Volume 5.djvu/524

 stratum, while the temperature of the American coast is lowered by the surging up against it of deep glacial underflow. The fact, he says, comes out most clearly from the Challenger soundings, which had been suspected by the United States Coast Surveyors, that the cold band which separates the Gulf Stream from the United States coast is really continuous with the cold strata that lie at some depth beneath the Gulf Stream, and this continuity explains the presence of the cold band which was previously wanting. For, as any flow of water from the equator toward either pole will tend toward the east in virtue of the excess of easterly momentum it brings from a part of the globe where its rotation was rapid; so any flow of water proceeding from either pole toward the equator will tend toward the west, in virtue of that deficiency of easterly momentum which it derives from a part of the globe where its rotation was less rapid. In this surging upward of the deeper and colder stratum lying beneath the Gulf Stream, we have very distinct evidence of its southerly movement. The precisely similar cold band which has been observed by Captain St. John to separate the Kuro Liwo, or warm Japan current, from the coast, may be fairly attributed to the same cause.

Action of Frost on the Position of Trees.—The elevation of the trunks of trees was the subject of some observations by Mr. Thomas Mechan at a recent meeting of the Philadelphia Academy of Sciences. On a previous occasion he had attributed this elevation to the natural thickening of the roots, which brought them in contact with unyielding rock beneath, the necessary consequence being that they would then lift the entire tree. Since that time he has been led to offer another explanation, viz., the action of frost. Most trees standing by themselves, he observed, have the collar of much greater diameter than the trunk above, and the upper portions of the roots, springing from about the collar, are considerably above the surface of the ground. That this is caused by the action of frost is rendered probable by what we know of its action on minor vegetation, what is called "drawing out." When the land freezes, expansion ensues, drawing up with it the roots of clover, and leaving of course a cavity from which the root was drawn. At the first thaw the liquid, carrying earthy matter, enters the cavity, and then the clover-root is prevented from descending to its original position. The same is true of trees. Roots, heaved up by frost, find the cavity beneath partially filled, and hence the tree will stand a little higher than before. Dr. Latham, State Botanist of Wisconsin, is of the opinion that large trees blow over much more readily than younger ones with the same, proportional weight of head to development of roots, chiefly because the older trees have been drawn nearer to the surface. One of the chief offices of the tap-roots is probably to prevent the tree being lifted too high by the frost. Dr. Mechan is inclined to think that the trees of tropical climates have by no means so great a development of taproots as those of more northern regions. This question he proposes to investigate further.

Topography of the Bed of the Pacific.—Soundings made by the United States Steamer Tuscarora, between San Diego, Cal., and Honolulu, S. I., show this part of the Pacific to be a basin with precipitous sides and a comparatively level bottom. In the first 100 miles west from San Diego, there appear to be two valleys and two peaks. The first valley is from 622 to 784 fathoms deep, the first peak 445 fathoms, the second valley 955 fathoms, and the second peak 566 fathoms. Thence a precipitous fall takes place, giving, in latitude 31° 43' north, longitude 119° 28' west (Greenwich), 115 miles from San Diego, a depth of 1,915 fathoms. After that there is a gentle slope, with comparatively unimportant interruptions, at the rate of three feet to the mile, to the point of greatest depth, 3,054 fathoms, at a distance of about 400 miles east of Honolulu. The sharpest elevation is a rise about midway between the United States and the Sandwich Islands, in latitude 26° 30' north, longitude 127° 37' west, the highest portion of which is 2,159 fathoms below the surface. At the next cast of the lead the valley to the west of this elevation took 2,650 fathoms. The fall of the side of the basin, east of Honolulu,