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Page:Popular Science Monthly Volume 18.djvu/590

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THE POPULAR SCIENCE MONTHLY.

ing of mathematics and the natural sciences in the grammar-classes be committed to special professors whenever the funds of the school will permit it and suitable teachers can be obtained; otherwise, professors of science in the higher classes may perform the duty for an additional compensation; or, if there is no other way, the ordinary professor may provisionally give the special instruction.

 

M. Faye's Theory of the Crust of the Earth.—M. Faye has propounded a new theory of the internal structure of the earth, an important feature of which is that its solid crust is much thicker under the seas than under the continental masses. The oscillations of the pendulum and the direction of the plumb-line are known to be subject to variations in consequence of the neighborhood of a mountain, or even of a hill, calculations based upon which enabled Maskelyne to determine the density of the globe. When, however, experiments with the plumb-line and pendulum were applied to table-lands and to the grander mountain-ranges, the deviations corresponding to the magnitude of the masses which were expected were not shown. The pendulum which is sensitive to the presence of the Great Pyramid of Egypt gives no sign of the neighborhood of the Himalayas. Further than this, a real deficiency of attraction has been observed upon continents, as if there were a great hollow under them; and the failure of mountain-masses to deflect the pendulum has been actually attributed to the existence of cavities in them. On the other hand, when the investigation is transferred to the sea, the weight is found to be too great, and is in excess of what is demanded by theory, as evidently it falls short of it on the continents. Hence, if we suppose that there is a lack of matter under the continents, we must also suppose that there is under the seas an accumulation of it above the average for the whole earth. M. Faye suggests, to account for these contradictions, that the cooling of the earth is going on faster and has taken place to a greater depth under the oceans than under the continents. The temperature at 12,000 feet of depth below the sea is a little higher than the freezing-point; at the same depth under the continental masses it is computed to be about 300°. The matter is kept at this temperature by the superior strata of earth almost impermeable to heat, and through which the heat that actually escapes is hardly perceptible. The crust of the earth in such a situation can increase in thickness only at the slowest. Under the sea, on the other hand, matter at the same depth is in almost immediate communication with a cold of the freezing-point, and, instead of having some non-conducting strata above it to prevent its escape, the heat is immediately absorbed in a cold of polar intensity. A similar difference exists deep in the beds of the submarine rocks, for the water is imbibed in their pores to a greater depth than in the sub-continental rocks, and the heat is conveyed away from them by the vertical convection of the warmed water rising in them. The more ancient the existing beds of the sea, the greater is the thickness of the crust that supports them as compared with that of the continents.

 

Trichinosis on a British School-ship.—A remarkable outbreak of trichinosis on the British reformatory school-ship Cornwall has recently been brought to the notice of the Government health boards. Up to the 23d of September last, the health of the boys had for a long time been good, but, between that day and October 23d, forty-three boys were taken sick, falling ill in batches—seven on the 23d, two on the 24th of September, sixteen between the 29th of September and the 1st of October, nine between the 3d and 6th, and the rest at intervals. The outbreak was regarded as one of enteric fever, and the general character and progress of the disease seemed to justify the view. No cause, however, likely to produce such an outbreak could be discovered. The hygienic condition of the ship was perfect. The inspector turned his attention to the food, and found that none of the officers, who were supplied with distinct food from the boys, were attacked. The boys from a particular mess suffered more than the others, and the tendency of the groups of fresh cases to occur on certain days of the week suggested a connection between the attacks and the salt pork that was served out on Mondays. The body of