Feb. in, i 885 I 



NA TURE 



375 



Another remarkable circumstan that the electric 



ted under abnormal conditions, viz. by the small number 

 of auroras appearing, which does not amount to one-tenth <>! the 

 normal number according to the latitude, and except in three 

 very feeble. ' ereof is to 



I li :ve, in the constantly falling snow and the 

 igh temperature. Even the diffuse luminous 

 seen so often during the winter oi 

 1882-83 (see my former report), and which gave the 

 il the aurora borealis, were very rare. 

 In fact, according to all reports, the characteristics of this 

 winter are quite contrary to the preceding one, which is the 

 1 we are now in a maximum period of auroral 

 There have indeed been very few evenings on 

 luminous phenomena could be studied, and the best 

 of them have nearly always been accompanied by a full moon. 

 as which the expedition has been able to make 

 henomena are therefore relatively small, 

 inly important. We know from our former experi- 

 ments that the " discharging-apparatus " produces a luminosity., 

 in the form of a cloud-light, sometimes in rays which rise 

 apparatus. The diffuse luminosity which always gave 

 the spectral reaction of the aurora was produced very easily. // 

 was aistiiictly seen above the apparatus at Sodanky 



■ with the naked eye, and very often with the spectro- 

 scope. 



As early as the autumn of 1SS2 Mr. Biese discovered that it was 

 11 3 spectral reaction of the aurora to the south- 

 I Si idankyla, a few degrees above the horizon, in the 

 directi in of the mountain Luostatunturi, while to traces were 

 visibl el ewhere. During the autumn of 1SS3 the same reaction 

 was sometimes obtained from the mountain IComattivaara, 

 il could not be perceived in the above-mentioned direc- 

 tion. This luminous phenomenon was also very distinctly 

 ib ei id on the following nights, viz. : — 



On the evening of November I, when a strong wind from the 

 west had chased away the clouds, an aurora was seen which com- 

 menced with a fairly regular arc in the north-north-west. The arc 

 touched the eastern horizon at about 20' north of Komatlivaara. 

 While the reaction was obtained along the whole length of this 

 arc, it entirely disappeared at this point of 20° from the horiz n 

 between the foot of the arc and the mountain. Moreover, this 

 was distinctly shown as the slit of the spectroscope was directed 

 towards the discharging-apparatus. On the southern side of the 

 mountain the reaction again disappeared completely. Asageneral 

 rule, the study of this luminous phenomenon was made at a dis- 

 tance of 5 km., but on two occasions rather closer. On November 

 12, in spite of the moonlight, moist air, and snow, a di tinct 

 reaction was obtained at a distance of 1 km. That evening the 

 phenomenon was very brilliant, appearing like a moving 

 luminosity along the whole apparatus, with a diffused radiating 

 fan of 1: I 1 lor fifteen minutes. 



At Kultala the luminous phenomena were generally of greater 

 intensity, but the majority of them could only be seen by means 

 1 cope, chiefly because on the most favourable 



occasions the moonlight was too bright. In order to obtain 

 another proof of the electric origin of the aurora borealis, the 

 expedition 1 with a double Iloltz machine, which, 



ii fragile construction, arrived safely at its destina- 



tion. When this machine was connected with the circuit of 

 \ i I., with the positive pole towards the earth, the 



I was more distinct. This was noticed as early as 

 December 17 at Sodankyla, when the machine was connected 

 with the c mdui toi from (Comattivaara, but the more exhaustive 

 studies were made at Kultala. The observations, which were 

 ile from the house (see the -ketch), have the follow- 

 . viz. : — 1884 : January 27, February 3, 4, 6, 7. 8, 12, 

 ■ ;. I hey were made by Mr. 

 have a report of each evening, that of February 3 being written 

 by me, the others by Mr. Biese. We detail below 

 February 3 and 7. 



iy 3. — Arrived at the Observatory at 6.30. The moon 

 had risen, ightly on the tops of the mountains ; no 



trace of the aurora could be seen either by the naked 



ope. At a telephonic signal the Holtz machine was 

 1 I with the conductor, the positive pole being placed 



towards the earth. But in spite of the closest attention no trace 

 of auroral light could be discovered. Presently, however, the 

 moon became covered with a haze (nimbus), and the brightness 

 of its rays diminished by om half; when this had lasted about 



half an hour, a luminous phenomenon in the shape of white 

 rose in flames from Apparatus I. This ^avc the reaction 

 in the spectroscope, and was very distinct, even to the naked eye. 

 At a signal, the machine was again put in motion, and now the 

 flames followed each other every time, giving the reaction in the 

 spectroscope. This reaction had sometimes a certain peculiarity : 

 although the slit of the spectroscope was very straight, the line 

 of the aurora was rather broad, and was followed by a con- 

 tinuous and very distinct spectrum towards F. At eight o'clock 

 the machine was stopped, and the fla-mes became fewer and 

 feebler. At S. 15 p.m. the machine was again put in motion, 

 with the same result as before. Presently a fog covered the 

 summit of the ^mountain, and the experiments, ceased at 

 S.40 p.m. 



February 7.— The clouds were about 5 C S. (5/10 cirro- 

 stratus), hence the reactions could only be obtained as pro- 

 jections upon the bright spectrum of the moon. Now and then 

 a very feeble reaction was obtained towards the north and west, 

 but the Apparatus I. gave none of them. However, when the 

 Iloltz machine was put in motion, a very distinct one was ob- 

 tained, particularly when sparks were emitted. After a Geissler 

 tube had been placed in the conductor of the machine the re- 

 action became still more intense, and was very distinct when 

 the discharge was accompanied by sparks. Never had I 

 obtained so intense a reaction. Mr. Biese again remarked 

 that no absorption-band had been observed near D in the spec- 

 trum of the moon, although its intensity varied considerably. 

 From these data may be inferred : — 



(1) That the "discharging-apparatus" produces on certain 

 occasions a diffuse light which gives the spectral reaction of the 

 aurora borealis. 



(2) That a Holtz machine placed in motion in the conductor 

 intensifies the phenomenon, if it already exists, and may even 

 produce it under favourable external conditions. 



(3) This luminous phenomenon is invisible to the naked eye if 

 the moonlight is very bright, but even then the spectroscope 

 often shows its pre ence. 



After my experience of the power of the " discharging-appara- 

 tus " to produce luminous phenomena in the form of rays, I 

 thought the phenomenon would appear easily. The following 

 conditions are however, I have discovered, necessary for this : 

 a clear sky, low temperatu e, and a relatively low barometer. 

 These conditions have been very rare this winter, and when they 

 have been present it was in an imperfect manner. However, 

 the phenomenon was seen twice, viz. on February 27 and 

 March 2, according to the following reports by Mr. Roos :— 



February 27, 18S4. — From the point o a feeble auroral arc 

 was observed extending from west to north-north-east, the in- 

 tensity of which gradually increased. At the same time there 

 appeared in the direction of Pietarintunturi, above the arc hut 

 not connected therewith, a sheaf of very intense ray-, which 

 moved rapidly westward and disappeared after passing the 

 northern line. Not a single ray was visible in any other part 

 of the sky. 



March 2. — Messrs. Granit, Ross, and myself observed from this 

 point an aurora whioh rapi lly increased in intensity, aadformed 

 a corona as early as 8 o'clock. I immediately went to point 

 III., in order that the luminous phenomena which might appear 

 above the apparatus at Pietarintunturi might be observed from 

 two points simultaneously. About 10.30 I perceived a very 

 intense ray in the direction of Apparatus I., leaning at first a 

 little tu the east, but rising by degrees like a radiating sheaf, 

 with a slight westerly direction. The phenomenon lasted from 

 thirty to forty seconds. On telephoning to Mr. Granit, who 

 remained at point O, he replied that no luminosity was visible 

 above the apparatus. Afterwards, and at short intervals, I three 

 time-, saw a feeble ray in the same direction, but of different 

 aspect. The ray, which was vertical, appeared of equal size and 

 ile yellow colour. Although feeble it was very distinct. 

 ling to Mr. Granit no rays could be observed from point 

 o, either above the apparatus or around the mountain for a 

 space of about 15 on either side, and on this occasion the moon- 

 light was very bright, wdiich, together with the intense aurora, 

 rendered the observation of the luminous phenomena very diffi- 

 cult, and besides this, the distance from o to I. is 2-45 km., while 

 from III. to I. it is only 1-56 km. 



If any doubt remained as to the first observation, i.e. as to 

 whether the rays were above the mountains or not, the second, 

 taken on March 2, is quite conclusive. If Mr. Granit cjuld 

 perceive no rays at point o, at a distance giving an angle of 15 



