Page:Popular Science Monthly Volume 10.djvu/650

632 upon the surface of the bergs was of dazzling whiteness, but, in places, faint discolorations, due not to earthy matter, but to the presence of birds, were observed. Prof. Thomson concludes that the ice from which the bergs were broken was found upon low, level land that was surrounded by shallow water.

Although no débris were seen upon the bergs, it is quite certain that large quantities of them were held in their under portions, whence they dropped into the sea, as such deposits were continually brought up by the dredge.

Prof. Thomson suggests that the increase of glaciers in thickness may be limited by melting at their under surface from pressure of the mass. A column of ice, 1,400 feet high, he estimates to lie upon the ground with a pressure of nearly a quarter of a ton to each square inch of surface, nor does he find reason to doubt that the temperature of the earth's surface beneath the glacier is about 32°. He cites the fact that from beneath glaciers in Greenland muddy streams are continually discharged. It is possible, therefore, that the antarctic glaciers, covering vast level tracts, are prevented from accumulating to a thickness much exceeding 1,400 feet, by waste in the bottom portions, where constant melting and regelation are going on.

On the chart of the American explorer, Lieutenant Wilkes, a position is given for what he called Termination Land. On closely approaching the spot, no land was found, and Prof. Thomson was "forced to the conclusion that Lieutenant Wilkes was in error."

The interesting fact was revealed by soundings that a layer of water 300 fathoms below the surface was warmer by several degrees than water at the surface, and it was ascertained that the heat increased northward. Hence it was concluded that the source of the warm water was northward, and that it may have been deflected by the southward projection of continental lands, turning southward currents which have their origin in the "great drift-current which sweeps round the globe."

Animals and Steam-Engines.—A writer in Dingler's Polytechnisches Journal, in noting the behavior of different animals toward the steam-engine, remarks upon the dexterity with which dogs run about among the wheels of a departing railway-train without suffering the least injury, whereas a host of railway workmen annually lose their lives. On the other hand, the ox, a proverbially stupid animal, continues standing composedly on the rails, having no idea of the danger which threatens him, and is run over. Many kinds of birds seem to have a peculiar delight in the steam-engine. It has often happened that larks have built their nests and reared their young under the switches of a much-traveled railway. In engine-houses the swallow is a frequent guest. In a certain mill, where a noisy, three hundred horse-power engine works night and day, two pairs of swallows have built their nests for years, and rear their young there regularly. A case of almost incredible trustfulness on the part of swallows occurred in the early part of last year, when a pair of these birds built in the paddle-box of a steamer, and regularly made the journeys from Pesth to Semlin. The author concludes with this caustic remark: "I have never yet found any animal at home in the boiler-house. Even the dog steers clear of boilers. It is almost as if the lower animals knew what an amount of stupidity and folly appears in our construction of boilers."

Prof. Dana on Cephalization.—The fifth of Prof. Dana's interesting papers on "Cephalization" is published in the American Journal of Science and Arts for October. The author's thesis here is that cephalization is a fundamental principle in the development of the system of animal life. As the animal grade rises, there is a compacting of structure in both the fore and hinder parts of the body. Of mammals the lowest forms are those having their locomotive functions in the posterior parts of the body, while in the higher forms the forces or force-organs are more and more forward in the structure. There are large size and strength behind in low forms, but a compacting of these and a better head in the higher.

The head becomes more and more the centre of nervous energy or force as development goes on, and this is to be seen in the specific forms of Nature. "Here form,"