smithsoniaj^ miscellaneous collectioxs. 



235 



INSTRUCTIONS 

 FOR OBSERVATIONS OF THUNDER STORMS. 



1. Give the time ot beginning and ending of the storm. 



2. Give the general direction of the approach of the storm, or the 

 point of the horizon where the storm cloud first appears. 



3. Give the direction of the wind before, at the time of, and after 

 the storm. 



4. Note the color of the lightning, particularly if it be violet, which 

 probably indicates a cloud of great elevation. 



5. Does the thunder cZourf frequently separate into two parts near 

 your residence ? If so, what is the topography of the surface 

 of the earth below? 



6. Record every instance of the striking of trees and other objects, 

 and every accident by lightning in your vicinity. 



v. Note the number of seconds the sound of a discharge continues 

 this will give approximately the length of the flash.* 



8. Note the time between the appea?-a7ice of the flash and the 

 hearing of the thunder; also the angle of elevation ; these will 

 give approximately the height of the cloud. 



9. Note the temp)erature of the air before and after the storm. 



10. Note the depsth and temperature of the rain immediately after 

 the storm. 



11. Note whether any hail fell, how long it continued, the form 

 and size of the hail-stones. 



* The velocity of sound at the temperature of G2° is 1125 feet a second, 

 or nearly a mile in 4^^ seconds. 



JOSEPH HENRY, 



Secretary of Siuithsonian Institution, 



