A. MATHEMATICS AND ASTRONOMY. 13 



longitudes will probably be laid next year through all^iberia 

 to Nicolajevsk, with which line the other stations of that 

 part of Russia can be easily joined either by telegraphic or 

 chronometric operations. 



With regard to photographic observations, Professor Struve 

 states that two observers, one at Vilna, and Dr. Vogel at 

 Bothkamp, in Holstein, have been perfectly successful in tak- 

 ing instantaneous observations with dry plates. 



NATURE OF THE AUROEA. 



Messrs. Heis and Flogel have lately published the result 

 of an elaborate series of investigations into the subject of the 

 aurora, and especially as to its altitude and its position in 

 space, and they sura up their conclusions in the following 

 propositions: 1. The aurora is a luminous phenomenon in re- 

 gions which are either entirely outside of our atmosphere, 01* 

 so situated that only the lowest portion enters into the out- 

 ermost strata of the atmosphere. The observed altitude of 

 the aurora varies from time to time, but the basal portion has 

 been determined to be at least forty miles in height, which, 

 of course, would preclude the idea of a direct association of 

 this phenomenon with clouds, or of the possibility of its in- 

 terposition between a distant mountain and the observer, as 

 has been asserted. 2. The largest portion of an aurora is a 

 luminous ocean of white light, which probably has its centre 

 in the magnetic pole, and thence may extend more or less to- 

 Avard the south. Its exact magnitude can only be determined 

 by corresponding observations in high northern and more 

 southern latitudes at a great distance apart. The depth of 

 this luminous stratum, or the distance between its upper and 

 lower borders, has not yet been ascertained. 3. This univer- 

 sal luminous ocean is bounded by a fringe, extending in the 

 direction of a magnetic parallel circle, which develops over a 

 more or less extended space the phenomena of rays, and which 

 seem to be exclusively limited to it ; the observer north of 

 the fringe seeing rays to the south of him, and the northern 

 sky exhibiting only a general white light. It is probable 

 that this border or fringe may have a width reaching 400 

 miles. 4. The fringe in general, shortly before a period of 

 radiation, is thrown out in the form of concentric waves of 

 light from the universal luminous ocean ; the non-luminous 



