142 SCIENTIFIC AGRICULTURE. 



thunder the noise which succeeds it: the difference in time 

 between the two phenomena depends upon the distance of the 

 explosion from the observer, allowing the velocity of sound to 

 be 1,125 feet, and that of light about 200,000 miles in a 

 second of time. We give below an extract from the " Ency- 

 clopedia Brittanica," showing the various conditions under 

 which electricity appears in the atmosphere. 

 "1. In regular thunder clouds. 

 " 2. During fog with small rain. 

 " 3. During a brisk snow or hail storm. 

 " 4. During a smart shower on a hot day. 

 " 5. During a shower on a cold day. 

 " 6. In hot weather after wet days. 

 " 7. In wet weather after dry days. 

 " 8. In clear and frosty weather. 

 " 9. In clear warm weather. 

 " 10. During a cloudy sky. 

 "11. During a mottled sky. 

 " 12. In sultry weather with light hazy clouds. 

 " 13. In cold, damp nights. 



" 14. During a north-west wind, which produces a sensation 

 of dryness and coldness, not indicated by the thermometer." 



WINDS. 



Wind is air put in motion. Rarefaction of one portion of 

 the atmosphere by heat, and condensation of another portion 

 by cold, are the principal causes of wind. Some local causes 

 of limited extent may produce wind, such as large fires, &c ; 

 but these winds are limited to the locality where they origi- 

 nate. There, is no known cause, besides heat and cold, which 

 is capable of producing any general or extensive current in the 

 air. 



A wind may be merely relative or apparent, and proceed 

 from the passage of the observer through the air, as by a 

 steam car or balloon. If the speed of his vehicle be twenty 



