Page:Popular Science Monthly Volume 41.djvu/582

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fectly developed cyclones and anti-cyclones. Ninety per cent of the cases occurred when the thermometer was between 28° and 31·9°, so that the greater number of cases occurred just before a thaw. The most common type of cloud which preceded both cyclonic and anti-cyclonic cases of silver thaw was cirrocumulus, frequently accompanied by cirrus and cirro-stratus; and the changes showed that the higher strata of the atmosphere came first under the influence of the moist current, which took from three to eight hours to descend to the height at which cumulo-stratus forms.


Our Destructive Locusts.—Eight kinds of destructive locusts are described in Prof. C. V. Riley's paper on that subject as infesting the United States or parts of its territory. The first is the Rocky Mountain locust (Caloptenus spretus), which has caused great destruction at times in its sudden, temporary appearances in the Western States and Territories. Its permanent breeding-ground, where it breeds every year and is always to be found in greater or less numbers, embraces the larger part of Montana, a narrow strip of western Dakota, all but the northwestern quarter of Wyoming, the central and northwestern parts of Colorado, small tracts in Utah, Oregon, and Idaho, and a large area in the British possessions north of Montana. The subpermanent region, where it is liable to breed for a few years and then disappear, lies immediately east of this; and the temporary region, where it appears for single seasons, includes large territories east and south of the subpermanent region. The lesser migratory locust (Caloptenus atlantis) breeds annually in abundance from middle Florida nearly to the Arctic Circle. It has been marked as injurious in New England in nineteen seasons since 1743. The nonmigratory red-legged locust (Caloptenus femur rubrum) has a common range with the previous species, but is rarer in the eastern part of its range, while it becomes abundant in the Mississippi Valley. It causes only local damage, and few cases of destructive appearance have been recorded. In common with the differential and two-striped locusts, it often gives cause for alarm by devastating grass-lands or growing crops. The California devastating locust (Caloptenus devastator) is a Pacific species, of which fifteen local destructive visitations are recorded. The differential locust (Caloptenus differ entialis) ranges through Illinois, Missouri, Nebraska, Kansas, and Iowa, and is found in Indiana, New Mexico, and California. Though not migratory, it is capable of making considerable flights, and is sometimes locally destructive. The two-striped locust (Caloptenus bivittatus) has an extensive range, covering most of the country. It is distinguished by its two lateral stripes reaching from the head to the extremities of the wing-covers. It often becomes locally abundant enough to do much damage to crops. The pellucid locust (Camnula pellueidd) occurs in the far West and in Maine, Massachusetts, Vermont, and Connecticut. The Eastern and Western forms used to be considered two species, but the difference between them is not appreciable. The American Acridium (Schistocerca americana) is our largest locust, being more than two inches and a half long. It occurs throughout the Southern States, through Mexico into Central America, and as far north as Illinois and Indiana. It is sedentary within the bounds of the United States, and becomes only locally destructive. Farther south, it is said to possess the migratory habit.


Objects of Forest Management.—Forest management, says Prof. B. F. Fernow, in his excellent paper on What is Forestry? has two objects in view, of which the first is to produce and reproduce a certain useful material, and the second to sustain or possibly improve certain advantageous natural conditions. In the first case we treat the forest as a crop which we harvest from the soil, taking care to devote the land to repeated reproduction of crops. In the second case we add to the first conception of the forest as a crop another, namely, that of a cover to the soil, which, under certain conditions and in certain locations, bears a very important relation to other conditions of life. The favorable influence which the forest growth exerts in preventing the washing of the soil and in retarding the torrential flow of water, and also in checking the winds and thereby reducing rapid evaporation further, in facilitating subterranean drainage and influencing climatic conditions, on account of which it is