1878] WRITINGS OF JOSEPH HENRY. 529 



OBSERVATIONS IN REGARD TO THUNDER-STORMS.* 

 (Journal of the American Electrical Society ; 1878 ; vol ii, pp. 1-8.) 



Dear Sir: I highly approve the object of your society; 

 and I beg leave to express the opinion that much valuable 

 information may be collected and preserved through its 

 organization, especially in regard to the phenomena of thun- 

 der-storms. 



For this purpose it might be well to prepare a series of 

 questions to direct attention to especial points of inquiry, 

 and I take the liberty of suggesting the following as a con- 

 tribution toward this end : 



A. — Particulars of the Storm. — ]. Give the number and 

 time of occurrence of thunder-storms, so as to show their 

 distribution through the months, days, and hours of the 

 year. 



2. Note the point of the horizon in which the storm gene- 

 rally arises in any given locality, and the point to which it 

 tends. 



3. Observe whether it usually divides into two storms at 

 any point. If so, what is the topography of the surface below ? 



4. Determine the width of the storm from the extent of 

 the surface covered by rain, and also (if possible by means 

 of the telegraph) the length of its path. 



5. Note the condition of the air before and after the storm 

 as to temperature, moisture, and pressure; also the tempera- 

 ture of the water which falls. 



6. Give the direction of the wind previous to the begin- 

 ning of the storm, during its continuance, and after its 

 ending. 



7. Observe whether a calm precedes the violent part of the 

 storm, and whether in front of it a curtain of dust is raised 

 to a considerable height in the air. 



* [A letter addressed to the corresponding secretary of the American Elec- 

 'trical Society, dated Washington, D. 0., October 13, 1877.] 

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