METEOROLOGY. THUNDER-STORMS. 495 



hour throughout the year ; so that an observer, placed at th ; equator, 

 were he endowed with orj^ans of sufficient delicacy, would never 

 lose the roll of the thunder. 



As tlie equator is quitted, the times at which rain falls become 

 less specific or periodical. Under tlie tropics, the rains of thunder- 

 storms, which are always the most copious, fall while the sun is in 

 the neighborhood of the zenith. In the northern hemisphere, the 

 greatest quantity of rain falls during winter ; and at places some- 

 what far south on the temperate zone, the summer rain is altogetner 

 irisigniiicant. In assuming the number 100 to express the whole 

 annual quantity of rain, we should have in 



Maileira. Lisbon. 



Winter 51 40 



• Spring 16 34 



Summer 3 3 



Autumn 30 23 



Less rain falls in the eastern parts of Europe than in the western. 

 The annual rain, too, is distributed very unequally over the different 

 seasons, as has been shown by M. Gasparin in a remarkable paper. 

 If we express by 100 the quantity of rain gauged in a year, we 

 should have for each season : 



In Uic west of West of East of Germany. St. Petersburg. 



Eng-land. France. France. 



Winter 21} 23 20 18 14 



Spring 20 13 23 22 18 



Summer 23 25 29 37 37 



Autumn 31 34 28 23 30 



The quantity of rain which falls in the course of a year varies 

 considerably according to the climate ; to form an idea of the extent 

 of these variations, it is enough to notice the results obtained at dif- 

 ferent observatories ; but it is less the annual quantity of rain that 

 falls, than the way or quantities in which it is distributed over the 

 different months of the year, which interests the farmer ; upon this 

 distribution, in fact, in many districts, depend the productiveness 

 and fertility of the soil. I add a table of the mean quantities of rain 

 in inches and lOths, that fall at London in the different months of 

 the year : 



Jan. Feb. March. April. May. June. July. Auj. Sept. Oct. Nov. Dec. 

 in. in. in. in. in. in. in. in. in. in. in. in. 



1.45 1.25 1.17 1.29 1.61 1.72 2.39 1.80 1.84 2.08 2.20 1.72 



<^ V. ON THE INFLUENCE OF AGRICULTURAL LABORS ON THE CLIMATE 

 OF A COUNTRY IN LESSENING STREAMS, ETC. 



A question of great importance, and that is frequently agitated a 

 this time, is, as to whether the agricultural labors of man are influ- 

 ential in modifying the climate of a country or not? Do extensive 

 clearings of woods, the draining and drying up of great swamps, 

 which certainly influence the distribution of heat during the differ- 

 ent seasons of the year, also exert an influence on the quantity of 

 runninsi water of a country, whether by lessening the quantity of 

 rain which falls, or by promoting the more speedy evaporation of 

 that which has fallen ? 



Id a:iae districts it has been held, that the streams which hat* 



