Page:Popular Science Monthly Volume 9.djvu/273

Rh and ants will be given to the public before long in a volume of the "International Scientific Series."

Sea-Soundings without a Line.—Dr. Siemens exhibited, at a recent meeting of the London Royal Society, an instrument devised by himself for ascertaining the depth of the sea. In explaining the principle of this instrument, Mr. Siemens observed that the total gravitation of the earth, as measured on its normal surface, is composed of the separate attractions of its parts, and that the attractive influence of each equal volume varies directly as its density and inversely as the square of its distance from the point of measurement. The density of sea-water being about 1.026, and that of the solid constituents composing the earth's crust about 2.763, it follows that an intervening depth of sea-water must exercise a sensible influence upon total gravitation if measured on the surface of the sea. His instrument, which he calls a bathometer, is described in the London Times as consisting "essentially of a vertical column of mercury, contained in a steel tube having cup-like extensions at both extremities, so as to increase the terminal area of the mercury. The lower cup is closed by means of a corrugated diaphragm of thin steel plate, and the weight of the column of mercury is balanced in the centre of the diaphragm by the elastic force derived from two carefully-tempered spiral steel springs of the same length as the mercury-column. One of the peculiarities of this mechanical arrangement is, that it is parathermal, the diminishing elastic force of the springs with rise of temperature being compensated by a similar decrease of potential of the mercury-column, which decrease depends upon the proportions given to the areas of the steel tube and its cup-like extensions."

The instrument is suspended in such a manner as to retain the vertical position, notwithstanding the motion of the ship, and the vertical oscillations of the mercury are almost entirely prevented by a local contraction of the mercury-column to a very small orifice. The reading of the instrument is effected by means of electrical contact, which is established between the end of a micrometer-screw and the centre of the elastic diaphragm. The pitch of the screw and the divisions in the rim are so proportioned that each division represents the diminution of gravity due to one fathom of depth. Actual experiment has shown the apparatus to be very reliable.

Formation of Mountain-Chains.—This subject is considered by Prof. Joseph Le Conte in the April number of the American Journal of Science, in which interesting facts are presented, the results of observations made by the author in the Coast Range of California. He finds that the actual length of the folded strata is about two and a half to three times the horizontal distance through the mountains. It thus appears that from fifteen to eighteen miles of strata, that is, of original sea-bottom, has been crushed or mashed into six miles, with "corresponding up-swelling of the whole mass."

This diminution of distance, according to the theory of Prof. Le Conte, has not arisen from folding of the strata, but by mashing of them by horizontal pressure.

From the flattened and elongated form of little nodules of clay found in some of the strata, he concludes that their elongation vertically exactly correlates their shortening horizontally, and that the one is to the other as two and a half or three is to one. It thus appears that in the compression of the beds their constituent particles underwent a change of form corresponding with the conditions of the pressure.

These clay pellets or nodules are supposed to have been formed on the bottom of gently-flowing streams, are a part of the original sedimentary beds, and are the same in character as those which form greenish spots in slate, as described by Prof. Tyndall.

It will be seen that, in accounting for the elevation of mountain-chains, Prof. Le Conte differs from Prof. Dana in this: that while they agree that mountain-chains are formed by yielding of the earth's crust, Prof. Dana attaches importance chiefly to the bending and plication of it, Prof. Le Conte to the crushing of it. He says, "I am satisfied that Prof. Dana greatly underestimates the amount of elevation by simple mashing as compared with folding."