374 



NA TURE 



[Feb. 19, 1885 



the atmosphere, i.e. from the zinc plate to the " discharging- 

 apparatus. " 



For the future I will call this direction of the current negative, 

 and the contrary direction from the atmosphere towards the 

 earth the positive. The deviations of the galvanometer were 

 very variable, and the variations characterised by sudden move- 

 ments, first in one direction, then in another. With this appa- 

 ratus observations were made at Sodankyla during last autumn 

 and winter. The deviation of the current was first exactly 

 noted, after which a Leclanche element was introduced 

 into the conductor, first with the positive pole towards the 

 earth, and then towards the mountain. By this process a 

 value was obtained at each observation of the electromotive 

 force in the circuit of the current. This consisted of two kinds, 

 viz. one arising from the contact of the zinc plate with "earth" 

 (here water), the other from the effect of the electricity in the 

 air upon the apparatus. The first kind varies very little. 

 Regarding the observations at Sodankyla it has been remarked 

 that they showed, as I have said, a negative current, which 

 however became sometimes positive in October and November, 

 and particularly when the aurora borealis was visible. 



The daily observations of the atmospheric current were made 

 at Kultala in the same manner as at Sodankyla. During the 

 months of January and February three more "discharging ap- 

 paratus" were constructed close to this station, and another 

 conducting wire was placed on Mascart insulators. Fig. 2 

 shows the position of the apparatus, whose elevation was as 

 follows : — 



Height above the River Ivalo Height above sea-level 



I. 324 metres ... 484 metres = 1630 feet 

 II. 334 ,, ... 494 » = 1664 „ 



III. 246 ,, ... 416 ,, = 1368 ,, 



IV - 253 .. •■• 4'3 .. = 1391 „ 



The distance between the station and the Apparatus I. was 

 3-626 km., and the distance between I. and II. 0-339 km. The 

 following points are also shown by this sketch, viz. : — 



o is a small observatory with a chimney ; o" is the point 

 where the conducting wires of the four apparatus were joined 

 to two wires leading to the station. 



\\ ith this apparatus numerous experiments were made, chiefly 

 in the month of March, of the results of which the following is 

 a brief resume : — 



(1) If two " discharging-apparatus " are placed at a given 

 elevation and connected with a galvanometer there is no current, 

 i.e. the deviation of the galvanometer equals o. 



(2) The Apparatus II., connected by a galvanometer to Appa- 

 ratus I., always gave a positive current, the strength of which 

 varied considerably. The following values selected as examples 

 show the electromotive force, expressed in volts, during four 

 days in March : — 



These values were obtained by introducing a Leclanche ele- 

 ment into the conductor in opposite directions. The elect in- 

 motive force of this element was determined by comparison 

 with a Daniell normal element. As there was a difference of 

 10 m. in the height of Apparatus II. and I., it may be noted 

 that the electromotive force varied during the above four days 

 between 0-0326 and 0-0053 volts per metre. The above two 

 results show, that the elet ti emotive force of I he elect 'lie currents of 

 the atmosphere may be studied with regard to their strength, and its 

 variations by means of two "discharging-apparatus" erected at 

 different elevations. 



When two apparatus at equal elevations give zero, it clearly 

 shows that the electromotive force observed only depends upon 

 the difference in elevation, i.e. that electricity is distributed 

 throughout the atmosphere, so that an electromotive force is 

 produced, causing a current from the atmosphere towards the 

 earth. The continued study with these four apparatus gave 

 this singular result : — 



(3) Close to the earth there is a stratum of positively electrified 

 air, the potential of which is greater than that of the imme- 

 diately overlying stratum, so that the potential diminishes from 

 the surface of the earth to a minimum, to again increase at 

 higher altitudes. The Apparatus III. and IV. situated in this 



stratum gave, combined with I. and II., a negative current, i.e. 

 from the earth to the atmosphere. 



This result, so soon arrived at, rendered rather difficult thi 

 projected work with the four apparatus, and the difficult) 

 increased still more owing to the fact that the conductive powei 

 of the air diminishes rapidly nearer the earth. In order to study 

 more minutely this peculiarity, two portable " discharging-appa- 

 ratus " were constructed, consisting of a cross of thin boards, on 

 which were placed several spirals of wires provided with points, 

 the total number of points being thirty. These miniature appa- 

 tus, which I will call S] and S 2 , were erected near II. upon 

 the most elevated point of Pietarintunturi, Sj being 2 m. above 

 the earth, and S 2 at the top of a pole 9/1 m. high. Both were 

 supported on Mascart insulators, and separately connected with 

 the stations by conducting wires. With this apparatus a current 

 was obtained from Sj and S.,, i.e. negative, from the earth to 

 the atmosphere. Great care was taken against any accidental 

 defect in the conductor, or in the arrangement of the apparatus. 

 The deviation obtained was very small, but quite measurable. 

 The actual experiments with these apparatus were made on 

 March 26 at 11 p.m., and lasted about three hours. As these 

 experiments are of great importance I will describe the method 

 followed. 



The night was chosen as the most favourable time, the wind 

 on the mountain being then very slight. The observers, Messrs. 

 Granit and Roos, having telephoned that the experiments could 

 commence, the current was measured by the galvanometer, S, 

 being then 2 m. and S„ at 9-1 m. above the earth ; the deviation 

 was negative. S 2 was then lowered to the same height as S,, 

 when the deviation was o. S L , was elevated to its former posi- 

 tion, and now the deviation was negative as originally. Sj was 

 now attached to two poles — 3 m. high — furnished with Mascart 

 insulators, and then raised by two men to a height of 4 m. The 

 deviation now became positive. 



This proved that the electric density of the stratum of air 

 diminishes up to the point at which the current changed, and 

 that the minimum density lay between a height of 2 m. and 

 4 m. 



It would have been very interesting to have continued these 

 experiments and further extended them, but this could not be 

 done, as the stay on the mountain became impossible. 



I went up on March 25 to examine the apparatus and con- 

 vince myself that no mistakes had been made, and although the 

 temperature was not more than - 12° C. it was impossible to work 

 except with the back to the wind, for if the face was turned 

 towards it, in a few moments the flesh became benumbed, and 

 breathing difficult and painful. On the mountain there was 

 nearly always wind, but its strength was less at night. 



These experiments with the portable apparatus will be 

 resumed next spring at Sodankyla under the superintendence of 

 Mr. Biese, but as it is very probable that the electric state of the 

 atmosphere will then be totally different, it is impossible to 

 foretell whether they will give the anticipated results. 



(4) From the stratum which lies some feet above the earth the 

 electromotive force increases with the differences in height of the 

 " discharging-apparatus." It has not been possible to determine 

 exactly the laws which regulate this increase, but it is believed 

 that the electromotive force increases more rapidly than in pro- 

 portion to the difference in height. 



The above results were obtained on clear days. The moisture 

 of the atmosphere affects the resistance of the conductors, and 

 appears also to act upon the electromotive force. 



On one of the small apparatus, S,, a number of points were fur- 

 nished with wicks soaked in petroleum ; when these were lighted 

 the effect was measured, and it appeared that the resistance 

 diminished a little, but the electromotive force remained un- 

 changed. Further results obtained from the observations must 

 tlepend on a detailed examination of the materials collected. 



Study of the Luminous Phenomena caused by tht " /'. 

 Apparatus." — Before passing to a final resume of the results of 

 these researches, I will refer in general terms to the meteoro- 

 logical character of the year, which are very important in relation 

 to this subject. It is very seldom that the winter in Lapland is so 

 mild as the last one was. There was not much rain or snow, but 

 it snowed nearly every day, so that the days when there was a 

 clear sky can easily be counted. It is only in perfectly clear 

 weather that the luminous electric phenomena are visible, and 

 this only happens when the moonlight is not too brilliant. 

 Consequently there were very few evenings when the luminous 

 phenomena could be successfully observed. 



