Page:Popular Science Monthly Volume 10.djvu/130

120 power of the north wind; and the same cause checks the growth of fungi. The economical value of the north wind is discernible in its power to preserve from rapid decay houses, barns, fences, etc., and the same influence must protect iron from destructive rusts.

Effects of Lightning on Different Species of Trees.—The effects of lightning on various species of trees have been made a subject of investigation by Daniel Colladon, who communicates to the Geneva Society of Natural History the results of his observations. He states that, when a poplar is struck, all the upper part of the tree remains perfectly sound and green. The height above the ground at which the injuries appear does not, in large poplars, exceed the third of the tree's height. These injuries commence immediately below the junction of the strong branches with the trunk. In general they do not reach quite to the ground. It is always the tallest poplar that is struck. In some cases the storm will pass over trees of other species, and will explode on poplars, though they be of less height. M. Colladon has never met with any traces of carbonization. The cases in which several poplars have been injured by a single discharge of lightning are rare. One such case is recorded by the author where three poplars were damaged by the same stroke. These trees stood in a straight line, and about twelve feet distant from each other.

How they teach Geology in Rome.—The eminent archaeologist, G. Mortillet, gives an amusing account of a class-lecture on geology which he once attended in the Roman University of the Sapienza. "I succeeded," he writes, "not without difficulty, in getting leave to be present at a lecture on geology. I was introduced into a large hall; in the middle stood a small table, at which four persons were seated. On the one side sat the professor in an arm-chair, and on the other three students in common chairs. Near the professor's seat was a more comfortable arm-chair for the inspecting prelate, who from time to time came to see that the teaching went on aright. As a stranger supposed to be well-disposed, I was honored with a seat in the grand armchair, I expected to listen to an interesting lecture in good Italian; the more, inasmuch as the professor, Ponzi, now a Senator of Italy, is a distinguished man, and a savant of repute. But I was disappointed. The professor, for upward of half the time of the lesson, was obliged to dictate—for such was the rule—his lecture, which had been written in advance in Latin, and revised and corrected by the censor. During the latter half he was permitted to give in Italian explanations of the dictated paragraphs; but he was not at liberty to diverge from his text, nor could the students take notes. These things I have seen with my own eyes at Rome under the reign of Pius IX., author of the 'Syllabus.' "

Effects of Compressed Air on Animals.—The mechanical effects of compressed air upon the animal economy, as ascertained by Bert, are to cause a lowering of the diaphragm and liver, and a consequent increased pulmonary vital capacity; this effect, while gradual in its production, lasts long after the subject is withdrawn from the compressed-air bath. Pravaz finds that the heart's action is at first increased, and then lessened, the pulse first becoming more rapid, and then slower, but never falling below the rate at normal pressure. The respirations are diminished during immersion, but on removal of the increased pressure they rise in frequency and in direct proportion to the degree of compression. There is an increase in the amount of urea excreted, but this increase diminishes the longer the sojourn in the compressed air. There is at the same time an increase in the amount of carbonic acid expired. The temperature of the body rises above the normal at first, and then falls as the immersion is prolonged. These varying effects are due, Pravaz thinks, to the two influences of inward atmospheric pressure and hyper-oxygenation, the former tending to diminish the circulation and the organic changes, and the other to increase them.

Occurrence of Nickel-Ores.—Nickel-ores occur in great abundance in New Caledonia, and are being actively worked. These ores in no way resemble those from which nickel