METEOROLOGY. 437 



distances from the earth's surface; that the light is generally white and 

 hiss often red or green, but in latitudes higher than Bergen it not un- 

 frequently presents spectral colors; and that the accompaniment oi 

 sound is an indisputable fact. Professor Tromholt still continues his 

 observations of the aurora borealis, to which he has devoted his atten- 

 tion for many years. It is his intention to make a catalogue of every 

 recorded manifestation of the northern light in Norway ; and for this 

 purpose he requests the co-operation of other observers, and will be 

 grateful for reference to any foreign sources of information, such as 

 ships' logs, journals, weather tables, almanacs, &c., which might yield 

 materials towards the better elucidation of this phenomenon. (Nature^ 

 XXIII, p. 84.) 



Prof. Sophus Tromholt has published a comple'te catalogue of auro- 

 ras observed in Northern Greenland from 1865 to 1880. He says that 

 at Godthaab the aurorse are seen almost exclusively in the southern 

 8ky and very rarely in the north, while at the southern part of Green- 

 land he has seen more intense aurorje throughout the whole sky. The 

 number of observed aurorte is directly proportionate to the brightness 

 of the sky, as shown by the following figures : 



Cloudiness ... l.G 1.7 1.8 1.8 . . 3.2 3.3 3.4 3.5 

 Aurone 7.0 7.0 5.0 6.0....2.9 2.7 2.5 1.5 



After reducing the observed auroras to what they would have been 

 at a uniformly clear sky he obtains the following series : 



No. solar spots 23.5 6.1 18.3 60.1 107.0 133.5 98.6 89.4 



No. aurorae 86.2 91.3 67.4 80.9 51.7 66.5 32.0 46.0 



No. solar spots 51.7 32.1 11.6 13.5 6.8 2.2 16.3 



No. aurorae .71.8 97.0 95.0 102.0 73.0 85.2 83.3 



The author finds that the location of the auroral belt is subject to 

 oscillations moving northward during the minimum solar spots and 

 southward during the maximum. {Nature, xxvi, p. 130.) 



Prof. Sophus Tromholt has for several years confined himself to the 

 investigation of auroras, and has published a monograph on that of 

 March, 1880, as well as a catalogue of those observed in Norway in 1878 

 and '79. He states that he will occupy Kautokeino (in Pinmark, Nor- 

 way), during the winter of 1882 and '83, in order to make corresponding 

 observations, and he earnestly advocates the establishment of special 

 aurora observatories. To this central institute, Drontheim, he would 

 have all Scandinavian observers report regularly. {Nature, xxvi, 

 pp. 220, 221.) 



XI. — a Refeaction and Mirage, b Halos. 



Glasenapp of Pulkova communicates preliminary results of study 

 into atmospheric refraction. The want of concentricity of sheets of air 

 of equal density produces a certain variation in the normal refraction 



