338 On the Auroral Beam of November 17, 1882. 



tions, the terrestrial current ceases below the aurora arc; while 

 the atmospheric current rapidly increases, but depends on the 

 area of the galvanic apparatus, to which it seems proportional. 

 In a letter to ' Nature ' (same volume, p. 389) Prof. Lem- 

 strom explains that the apparatus was constructed of uncovered 

 copper wire provided at each half metre with fine erected 

 points. The wire was led in slings to the top of the hill, and 

 reposed on the usual telegraph insulators. From one end of 

 this wire was conducted a covered copper wire on insulators 

 to the foot of the hill 600 feet high, which there joined a plate 

 of zinc interred in the earth, and in the circuit was put a gal- 

 vanometer (no battery is mentioned, J. R. C). This apparatus 

 produced the halo at Orantunturi and the straight beam at 

 Pictarintunturi as the positive current in the galvanometer 

 at both places. The terrestrial current diminishes (or ceases) 

 below the belt of maxima of the aurora. 



In the ' Daily Telegraph' newspaper of March 1st, 1883, 

 Prof. Foerster is stated to have given an account of these ex- 

 periments, and to have added that the astounding result was 

 the formation of an aurora borealis rising above the mountain- 

 top to an elevation estimated at 300 feet. In a subsequent 

 number of the same paper (March 5th), under a heading " Arti- 

 ficial Aurora," an article is found which alludes in detail to 

 several points in connexion with the phenomena involved, 

 but which to my mind are those really requiring further ex- 

 planation. One of these is the direct comparison of the electric 

 glow in an exhausted receiver with the auroral discharge. It 

 may be conceded that the two look alike; but it is well known 

 that here the comparison ceases, as every effort has been made 

 for years past, without success, to obtain the aurora-spectrum 

 from such a source. Next, the phenomena are attributed to 

 atmospheric electricity; but in point of fact it is strong mani- 

 festations of earth-currents, and not of atmospheric electricity, 

 which have generally accompanied auroral displays, notably 

 that of November 17th last. Again, while Prof. Lemstrom's 

 actual aurora and Plante's artificial auroras are alluded to in 

 the article in question as connected with the positive pole, it 

 was in the glow of the negative, or violet pole, that the late 



o 



Prof. Angstrom sought for, and considered he had obtained, 

 an aurora-spectrum. 



With regard to the spectrum obtained by Prof. Lemstrom, 

 if the instrumental resources were adequate for exact measure- 

 ment, the observation obtained from such a source is doubtless 

 reliable ; but it should, by way of precaution, be remembered 



o 



that even scientists of such calibre as Angstrom and Respighi 



