530 WRITINGS OF JOSEPH HENRY. [1878 



8. Note the number of seconds the sound of a discharge 

 continues, which will give approximately the minimum 

 length of its path,* 



9. Note the time between the appearance of the flash and 

 the sound of the thunder, and also the angle of elevation ; 

 these will give approximately the height of the cloud. 



10. Ascertain whether any hail accompanies the storm ; 

 if it does, note whether it falls along in two tracks or in one. 

 In the former case, give the distance between the tracks. 

 Give the size and character of the hail, whether it consists 

 of an agglomeration of crystals, or of rounded masses strati- 

 fied with clear ice and snowy concretions, and whether it 

 contains in some cases small particles of dust or sand, 



11. Note the number of discharges between the different 

 parts of the same or different clouds, and also between the 

 cloud and the earth. The former will probably be more 

 frequent than the latter. 



12. Note the color of the lightning, particularly if it be 

 violet or purplish, which will probably indicate a cloud of 

 great elevation. 



B. — Effects of the Electric Discharge. — 1. State what kind of 

 trees are struck, and on what parts of the tree the effects are 

 most apparent — on the branches, or the trunk. 



2. What are the mechanical effects observed in the tree ; 

 is it torn asunder laterally, or is it broken transversely to the 

 axis, or both ? 



3. Was the tree green or dry? 



4. When a house is struck, state if it had a lightning-rod, 

 and, if so, give its character, and especially its connection 

 with the ground. 



5. Mention the part of the house struck. If the chimney, 

 was there fire in it at the time? Give the path of the dis- 

 charge through the house, and its relation to conducting 

 metals. 



6. Note the inductive effects of the discharge in produc- 



* The velocity of sound in open air at the temperature of 62° Fahr. is 

 1,125 feet a second, or nearly a mile in four and seven-tenths seconds. 



