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THE POPULAR SCIENCE MONTHLY. 



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 cirro- 

 cumulus, 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. 



Onr Destructive Locusts. Eight kinds 

 of destructive locusts are described in Prof. 

 C. V. Riley's paper on that subject as infest- 

 ing the United States or parts of its territory. 

 The first is the Rocky Mountain locust (Ca- 

 loptenus spretus), which has caused great de- 

 struction at times in its sudden, temporary 

 appearances in the Western States and Ter- 

 ritories. 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 north- 

 western 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 tem- 

 porary 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 abimdance from middle 

 Florida nearly to the Arctic Circle. It has 

 been marked as injurious in New England 

 in nineteen seasons since 1*743. The non- 

 migratory red-legged locust (Caloptenus fe- 

 mur 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 lo- 

 cal damage, and few cases of destructive ap- 

 pearance 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 Califor- 

 nia devastating locust (Caloptenus devastator) 



is a Pacific species, of which fifteen local de- 

 structive visitations are recorded. The differ- 

 ential locust ( Caloptenus differ entialis) ranges 

 through Dlinois, Missouri, Nebraska, Kansas, 

 and Iowa, and is found in Indiana, New 

 Mexico, and California. Though not migra- 

 tory, 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 lat- 

 eral stripes reaching from the head to the ex- 

 tremities of the wing-covers. It often be- 

 comes locally abundant enough to do much 

 damage to crops. The pellucid locust ( Cam- 

 nula peUueidd) occurs in the far West and 

 in Maine, Massachusetts, Vermont, and Con- 

 necticut. The Eastern and Western forms 

 used to be considered two species, but the 

 difference between them is not appreciable. 

 The American Acridium (Schistocerca ameri- 

 cana) 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 Dlinois and Indiana. It is seden- 

 tary 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 mate- 

 rial, and the second to sustain or possibly im- 

 prove certain advantageous natural condi- 

 tions. 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 fa- 

 vorable influence which the forest growth ex- 

 erts in preventing the washing of the soil 

 and in retarding the torrential flow of water, 

 and also in checking the winds and thereby re- 

 ducing rapid evaporation further, in facili- 

 tating subterranean drainage and influencing 

 climatic conditions, on account of which it is 



