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THE POPULAR SCIENCE MONTHLY. 



The British Association. The fifty-sec- 

 ond meeting of the British Association will 

 be held at Southampton, beginning August 

 28d, when the chair will be resigned by Sir 

 John Lubbock and assumed by Dr. C. W. 

 Siemens, F. R. S., president-elect, with the 

 usual address appropriate to the occasion. 

 The addresses at the evening general meet- 

 ings will be, " On the Tides," by Sir Will- 

 iam Thomson, F. R. S., August 25th, and 

 on " Pelagic Life," by Professor H. N. 

 Moseley, August 28th. The presidents of 

 the sections will be : A, Mathematical and 

 Physical Science, Lord Rayleigh ; B, Chemi- 

 cal Science, Professor D. Liveing ; C, Geol- 

 ogy, R. Etheridge, F. R. S. ; D, Biology, 

 Professor A. Gamgee, with Professors Gam- 

 gee, M. A. Lawson, and W. Boyd Dawkins 

 as presidents in the Departments of Anat- 

 omy and Physiology, Zoology and Botany, 

 and Anthropology ; E, Geography, Sir R. 

 Temple, Bart. ; F, Economical Science and 

 Statistics, the Right Hon. G. Sclater-Booth ; 

 and G, Mechanical Science, John Fowler, 

 F. G. S. Excursions to places of interest 

 in the neighborhood of Southampton will 

 be made on the afternoon of Saturday, Au- 

 gust 26th, and on Thursday, August 31st. 



Forests and Climate. Dr. J. M. Anders, 



in the "American Naturalist," has carefully 

 examined the influence of forests upon cli- 

 mate and rain-fall. The principal influence 

 exerted by woods upon climate is as wind- 

 breaks, in which capacity the service they 

 render is familiar enough. The experiment 

 has been tried extensively in France of 

 planting trees in belts one hundred metres 

 apart, with marked benefit to the climate. 

 Forests may slightly promote the condensa- 

 tion of moisture by inducing an upward 

 movement of the air, as mountains are 

 known to do on an extensive scale ; but 

 their action in this respect, on account of 

 their low height, is not important enough 

 to be made account of. Woods play a more 

 important part in furnishing the air with 

 moisture by transpiration of water through 

 their leaves. It is computed from experi- 

 mental tests that they give off in this way 

 twelve times as much water as is evaporated 

 directly from the soil on which they stand, 

 twice as much as goes up from a free soil, 

 and more than is emitted from an equal 



body of water. They are able to do this, 

 and keep it up, because they are at all times 

 supplied with an abundant store of moist- 

 ure for transpiration. This is given them 

 partly by the power which their roots have 

 to attract moisture from every direction ; 

 partly by the retention of the rain-fall in 

 their net-work ; and partly by the property 

 possessed by vegetable mold of absorbing 

 moisture and holding it. This power of 

 evaporation is shared by the humbler vege- 

 tation, and it operates nearly constantly, 

 even during long droughts. Climate is also 

 materially affected by this quality, for moist 

 air during winter tends to moderate extreme 

 cold and during summer produces a refresh- 

 ing coolness. Now, since it is established 

 that forests moisten the air over, in, and to 

 some extent around themselves, "may we 

 not be pardoned for concluding that warm 

 currents sweeping over a country and strik- 

 ing the cool moist air in and above the for- 

 ests, and mingling with it, would have a 

 portion, at least, of the contained moisture 

 condensed into gentle showers, extending 

 their beneficent influence to neighboring 

 fields ? Again, let some stray current come 

 along, of a lower temperature than the air 

 of the forest, and the moist air of the for- 

 est would readily be condensed, since it is a 

 well-known fact that a moist air discharges 

 its vapor more readily in the form of rain 

 than a drier atmosphere. We have now 

 seen how trees can cause local rains ; it will 

 also be observed that the rain is formed 

 chiefly above the forest, though it may be 

 through the influence of winds that it falls 

 to the earth for some distance around. By 

 increasing the frequency of light rains, for- 

 ests tend to obviate drought, which is of 

 ultimate importance to the farmer's crops 

 and vegetation in general. It will be seen 

 that all our deductions have been drawn 

 largely from the known facts from observa- 

 tions." Forests also produce abundant dews, 

 an office not to be despised, for heavy dews 

 are often very refreshing to vegetation. 



Atmospheric Pressure and the Sea-Lev- 

 el. One of the most interesting phenom- 

 ena of the recent winter in Europe was a 

 remarkable depression of the level of the 

 Mediterranean Sea under the influence of 

 the high barometric pressures of December 



