446 Chronicles of Science. [July, 



Annual Pressure in Scotland." He has investigated the returns 

 from fifteen stations for eleven years, and the results obtained 

 afford, as might be expected, a strong corroboration of the principle 

 that the motion of the air is related to the differences of atmo- 

 spherical pressure. The mean annual pressure decreases from east 

 to west and from south to north, and as the wind always blows 

 with the lowest barometrical reading on its left hand side, we see 

 that the general conditions of pressui-e hie in harmony with the 

 fact that our prevalent winds are south-westerly. 



The monthly curves exhibit three minima and three maxima; 

 the former occurring in January, March, and October ; the latter 

 in February, May, and November. 



The depression in January increases as we go northwards, while 

 that in March changes in the opposite direction. In October the 

 decrease is nearly uniform over the whole of Western Europe. 



As regards the maxima, that in February is of slight extent. 

 In May the absolute maximum for the year is reached, corresponding 

 to the period of prevalence of our east winds. The increase of 

 pressure in November is the phenomenon so long noted as the 

 gi'eat November wave, to which it is not now the fashion to attribute 

 nearly so great an influence on our weather as it was some few 

 years ago. This paper is a very useful contribution to meteorology, 

 as the results of eleven years' observations may be fairly considered 

 as worthy of attention. 



The 'Atlas Meteorologique ' for 1867, published by the Ob- 

 servatoire Imperial, contains an elaborate paper by M. Becquerel, 

 on the influence of forests on climate. The paper is very carefully 

 written, but on reading it proves somewhat disappointing, as it 

 leads to very few practical results, owing to a deficiency of evidence 

 on many questions. 



There is one action which all vegetation, of whatever character 

 it be, exerts, and that is the protection of the soil on which it grows 

 from forcible removal by floods. The roots traverse the earth in 

 all directions, and bind it together, while the branches break the 

 force of the rain as it falls. As soon as a hill-side is cleared of 

 forests, the rivulet-beds are scored deeper and deeper, and the soil 

 is gradually washed down, leaving the rocks bare. Tlie roots of 

 trees liave, in addition, a tendency to facilitate the percolation of 

 water to the subsoil, and thus to prevent its accumulation on the 

 surface, and the consequent production of swamps, such as have 

 been formed in parts of France within historic times. There is 

 another beneficial effect produced by trees, that of impeding the 

 motion of the air, and thus aflbrding shelter from wind. This 

 action is, of course, limited, depending on the height of the trees 

 and the direction of motion of the wind. If this direction be 

 horizontal the shelter afforded is very considerable, as it has been 



