818 



SCIENCE 



[N. S. Vol. XLIV. No. 1145 



In the display of August 28, they were of 

 various colors; in that of September 1 they 

 were of a uniform red. The brightness seemed 

 to be about the same in both cases, and suffi- 

 cient for one to read a printed page with ease. 

 There was no moon. The southern streamers, 

 especially, were very changeable; having con- 

 tinually many of what were then called " merry 

 dancers," or rapidly changing clouds of light, 

 among them. These displays, as it was noticed 

 in the papers at the time, were visible as far 

 south as Cuba ; though of course they were not 

 there so brilliant. They were accompanied by 

 magnetic storms, and interference with tele- 

 graphic work. 



The present writer was then engaged in as- 

 tronomical observations, which had to be sus- 

 pended during these illuminations. 



Geo. M. Searle 



Apostolic Mission House, 

 Brookland P. O., "Washington, D. C. 



INFERENCES CONCERNING AURORAS 



To the Editor op Science: I was much 

 interested in the vivid description of the 

 aurora of August 26 given by Dr. C. C. 

 Nutting, followed as it was in the next issue 

 of Science by a number of letters from differ- 

 ent localities concerning the same, and I find 

 in the last issue of Science, that of November 

 17, a most interesting account of this aurora, 

 with general considerations respecting this 

 phenomenon, given by Professor C. C. Trow- 

 bridge, of Columbia University. 



Inasmuch as I had some time ago prepared 

 a paper entitled " Inferences Concerning 

 Auroras " for presentation at the meeting of 

 the National Academy of Sciences in Boston, 

 where the paper was read on November 14, it 

 may be of interest to make a few brief state- 

 ments concerning the inferences presented. 

 In an address at the opening of the Palmer 

 Laboratory of Physics at Princeton, entitled 

 " Atmospheric Electricity " which appears in 

 Science, N. S., Vol. 30, No. 781, pp. 857-869, 

 December 17, 1909, I took occasion to state 

 some opinions based upon the observation of 

 auroras for many years, particularly as to the 

 general relation of the auroral streamers to 

 the earth. I quote the following statement: 



I have come to the opinion that the auroral 

 streamers often extend in a general direction out- 

 wardly from the earth, sometimes for very great 

 distances relatively to the known extent of our 

 atmosphere. The effects observed appear unac- 

 countable on any other supposition, while they are 

 consistent with the idea of outwardly directed 

 streams of great extent. 



The evidence furnished by the recent aurora 

 of August 26 confirmed the inferences which 

 I had made many years ago, and added con- 

 siderably to the possibility of applying certain 

 ideas in explanation of auroral phenomena 

 generally. In the paper before the National 

 Academy I have, I think, established with a 

 fair degree of certainty that the auroral 

 streamers are in reality vertical or approxi- 

 mately vertical to the earth's surface. These 

 vertical streamers appear in bands, more or 

 less wide, in the general direction of parallels 

 of latitude forming belts or zones in which the 

 streamers extend upward, somewhat like trees 

 in a forest. I find an explanation, also, of 

 those auroras which appear to be limited to a 

 narrow belt, and appear as a single narrow 

 streak of light across the sky from east to west. 

 There may be, of course, in any aurora, a num- 

 ber of such belts occupying different latitudes. 

 I have endeavored to show, and I think suc- 

 cessfully, that the curvature of the so-called 

 auroral arch is a purely optical effect of per- 

 spective, increased somewhat by the curvature 

 of the earth, and that the appearance of folded 

 curtains of streamers merely means that the 

 lower ends or feet of the streamers which are, 

 with relation to the observer, of varying alti- 

 tude, or are of varying latitude as in a belt 

 which is of a winding nature. 



It is pointed out, also, that the convergence 

 of long streamers towards the zenith seen in 

 the great auroras is purely an optical effect of 

 perspective, and that the so-called zenith 

 crown is, in reality, due to bundles of stream- 

 ers nearly vertical like the others, but seen on 

 end overhead. 



There are a number of other inferences 

 which are supported by the observations of 

 Carl Stormer and others, among which is the 

 probable existence of a conducting layer at a 



