98 



which circumstances oceured very seldom during the winter 

 1883 — 84 and besides a frequent rain- and snow fall seems 

 to have diminished the intensity of the eleclrical forces in 

 the atmosphere. 



During all observations on the luminous phenomena, 

 we executed measurements of the EMF of the el. air-current, 

 already 1871 in Enare. Absolutely taken the EMF was very 

 little, tenthe of volt, especially in comparison with the elec- 

 trometic results, ten to several hundred volts. This state 

 was, however, confirmed during 1882 — 84. From this fact 

 we can deduce the great difference between a measurement 

 of the potential in a point of the atmosphere with the elee- 

 trometer and measurement by means of the point-apparatus 

 of the EMF which produces the electric air-current from the 

 atmosphere to the earth. 



All the efforts made during the autumn and winter 

 1882 — 83 to observe the luminous phenomena and measure 

 the electric forces of the air-current, ended with the con- 

 tinuation of the observations during the following year, the 

 results of which are cited in art 5. 



A much disputed question is the height of the aurora 

 above the earth-surface. Most different heights have been 

 calculated from a few km to eight hundred and thousand 

 out of observations after several methods. 



The finnish polar-expedition gave an important contri- 

 bution to the solution of the question. Observations were 

 made on a base of only 4,5 km. Though the phenomenon 

 was seen on the northern sky, we received in Sodankylä, at 

 the southern end of the base, greater angles between the 

 sightline and the horizontal plan, than in the northern end 

 of the base or the absurd result that the phenomenon was 

 at infinite distance. As the both observatörs could commu- 

 nicate by thelephon no mistakc was possible. The fact is 



