OF ARTS AND SCIENCES. 129 



IV. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 HARVARD COLLEGE. 



XXV. — ATMOSPHERIC ELECTRICITY AT HIGH 

 ALTITUDES. 



By Alexander McAdie, M.A. 



Communicated June, 1885. 



The following experiments were made at Blue Hill Observatory 

 during the month of June, 1885. The summit of the Hill has an ele- 

 vation of 635 feet above sea level, and is therefore the highest point 

 on this section of the Atlantic seaboard. With the exception of the 

 two or three other hills in the range, all the surrounding country is 

 very low and level. The average elevation is below 100 feet. On 

 all sides this low land is well watered, having rivers of fair size and 

 many ponds. For these reasons it was thought profitable to make 

 some observations on the electrical state of the atmosphere, similar in 

 nature to a series made for the United States Signal Service at the 

 Jefferson Physical Laboratory in Cambridge. 



The following apparatus was taken to the summit, and employed as 

 hereafter described : — 



A Multiple Quadrant Electrometer, designed by Professor Trow- 

 bridge, a description of which may be found in the Proceedings of the 

 American Academy, June, 1885. 



A portable battery of 100 Beetz cells, set up in series. 



A second battery of the same kind, the cells arranged for con- 

 venience in sets of ten. 



A newly set up Daniell cell. 



Two large light kites, silk-covered and tinfoiled on the front face ; 

 the longest axes of the kites being over 4 feet. 



1,500 feet of strong hemp fish-line, around which in a close spiral 

 was wound No. 22 uncovered copper wire. 



50 feet of insulated office wire, and some 10 or 12 feet of rubber 

 tubing, to better insulate the office wire. 



VOL. XXI. (N. S. XIII.) 9 



