Page:Popular Science Monthly Volume 31.djvu/299

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free from ice at that time. This immigration must have taken place during repeated changes of climate. "After several thousands of years with a severer climate that favored the immigration and extension of northern and eastern species, other thousands of years followed with a milder climate. During this period fresh immigrants came from the south and southwest, compelling the older flora to retreat. In this manner the climate must have changed several times since the Glacial age, and the distribution of the plants must have changed in accordance therewith. The periods of variation are reflected in the present flora, and it is the former which have led to the great gaps in the extension of coast as well as inland plants. The sunny screes, the slate districts, and the moist coast tracts, are asylums where the different floras have found refuge. In the intermediate parts they have been dislodged by the new-comers. But certain species, being indifferent to the variations, extended constantly, at the expense of others, and this is the reason of the Norwegian flora being so monotonous."


Artificial Digestion.—O. Petersen, of St. Petersburg, has made experiments to ascertain the influence of certain medicines on digestion. The problem he set himself to determine was the time required to digest from 20 to 40 grammes of dried albumen by the aid of 450 centigrammes of a specially prepared artificial gastric fluid. Alcohol in the proportion of five per cent did not hinder digestion, but the process was retarded as the percentage rose, and stopped at ten per cent of alcohol. Antipyrin, in light doses, was without influence, but in larger quantities slightly retarded the action. One or two grammes of bromide or iodide of potassium hindered the process a little. The organic preparations of iron scarcely affected the time required for the digestion, while reduced iron and the inorganic salts slowed the action, as did also magnesium and sodium sulphates, even in moderate doses. A gramme-dose of chloral hydrate had no slowing effect, though a marked retardation occurred with a dose of a gramme and a half. Chloride of sodium did not retard digestion, even when employed in large doses.



A series of charts, showing the surface temperatures of the Atlantic coast waters, from Maine to Florida, is under preparation by the United States Fish Commission, assisted by the Lighthouse Board and Signal Service. Observations, covering five years in time, have thus far been made at twenty-four lighthouse-stations. The temperatures at the several stations are shown for each year by ten-day means, and in such a manner as to give the isothermal relations of the stations.

It is said, on the authority of "an American railway engineer," that low temperatures do not decrease the strength of rails, as is commonly supposed, although it is true that accidents are more likely to occur from broken rails in cold weather. This is because, when the ground is frozen hard, it loses its elasticity. Nevertheless, something must yield when the train rune over the road; it is the ground that yields in unfrozen weather; but during a freeze the ground will not yield, and the rail, as being the weakest part of the structure, has to suffer the consequences.

Mr. Blanford, in his report on the "Administration of the Meteorological Department of India" for 1885-'86, describes the steps which have been taken in the peninsula to discover to what extent forests influence the rainfall. A few observatories have been established in the Ajmere forests, and the results so far have been to show slightly but appreciably higher rainfall in the forests than without. It is admitted that more careful inquiry must be made before any definite conclusions can be drawn. Mr. Blanford points out that M. Woeikoff, in a paper on the subject with special reference to India, essentially supports the view, which he himself regards as probable.

The Paris Academy of Medicine has been discussing the bad results of mental strain on young persons. A particularly hard bearing of the process was shown upon French girls, twelve thousand of whom are competing for diplomas entitling them to two thousand appointments in government schools.

Professor Sargent, Director of the Arnold Arboretum, of Harvard College, estimates that five foreign trees are planted in New England to one native. Yet, of all foreign trees introduced into America, the willow alone, he thinks, has qualities not possessed in a greater degree by some native. The European oak, and the Scotch, Austrian, and Corsican pines all die at about the time when they should be at their prime, and the Norway spruce, at a corresponding age, is decrepit and unsightly.