Dec. 1 6, 1 8 So] 



NATURE 



149 



light increased in frequency and brilliancy, and at 1 1.25 

 they might be described as broad flashes overspreading 

 a large part of the northern half of the sky, always 

 travelling upwards, and sometimes passing the zenith. 

 The main body of streamers had by this time mostly 

 faded, after going through an extraordinary series of 

 changes which I found it quite impossible to record. 

 Every minute or two new rays would strike up to the 

 zenith, or sometimes beyond, and every now and then a 

 portion of an older ray would suddenly shine out with a 

 kind of phosphoric light. 



The display now rapidly faded, and though at 11.35 

 and again about 11.45 there were minor reappearances of 

 rays, the aurora seemed to be near its end, and I returned 

 home. 



The brightness of the phenomenon was somewhat 

 delusive ; for when a superb corona of rays covered the 

 northern sky, I could only just read my watch by its 

 light, and could not read what I endeavoured to write 

 down on paper. The light was either white or of a 

 greenish yellow tinge. There was no trace of the redness 

 or other colours seen on other occasions. 



By very good fortune I was able to watch the aurora 

 of the next night (August 13) under the moit favourable 

 possible circumstances, namely, while steaming down the 

 Christiania Fyord, in the steamship Angela, during a 

 beautiful calm evening. The aurora began at 10.20 p.m. 

 with a very faint uniform arch, or rather line of white 

 light, appearing 8° or 10° above the horizon, with difficulty 

 distinguished from the twilight. This soon faded away 

 entirely ; but at 10.35 reappeared as a very distinct 

 luminous arch, separated by a dark space from the twi- 

 light. Some slight signs of rays now also appeared. 



At 10.45 the arch seemed to be rising somewhat, with- 

 out ever attaining a height of more than about 15°. The 

 lower edge became indented by r.ay-like notches. There 

 was a tendency to the formation of streamers at the flanks. 

 At 10.50 a fine single ray shot up from the horizon right 

 through the arch, at 10° to west of true north. Streamers 

 also began to appear above the arch, and especially at its 

 eastern end ; but the streamers were in no way comparable 

 to those of the previous night. The arch now began to 

 lose its previous regular form, and to go through a re- 

 markable series of gradual changes and contortions, 

 which it is impossible to describe. By degrees the eastern 

 end became incurved in the manner of a folded curtain 

 (like the pictures of auroras in the PoLnr regions which 

 we see in books), and a few fragments of rays tended to 

 form an inferior arch. 



For more than an hour the light of this aurora was 

 steady; but about 11.30 p.m. pulsations first began to 

 appear faintly, soon increasing in frequency and width. 

 As the pulsations grew the arch almost insensibly disap- 

 peared, but patches of light and fragments of rays 

 occupied the sky above where the arch had been, and 

 were every instant lighted up, as it were, by the passing 

 coruscations. These flashes of light became more and 

 more frequent, following each other every second, or even 

 several times in a second, so as to produce at last a kind 

 of rustling or dancing appearance. They were most 

 intense upon the rays and patches, but were not confined 

 to them. At 12.30 the display was failing, the waves 

 being less frequent. At i a.m. there remained only a few 

 irregular patches of faint, steady light, with occasional 

 flashing waves. The light was again white, or greenish 

 yellow. On neither occasion did the aurora seem to have 

 the slightest relation to the ordinary vaporous clouds of 

 the atmosphere, nor did the dark space beneath the arch 

 seem to be more than might be explained as the effect of 

 contrast. 



Mr. Thomas Bennett, who is well known to all Nor- 

 wegian travellers, and has resided many years in Christi- 

 ania, informed me that the aurora of the 12th was 

 probably the finest he had ever seen among the many 



grand displays which occur in Norway. Though I have 

 witnessed several fine auroras, including some of those 

 seen in the United States in August and September, 1859, 

 and two fine displays of the Aurora Australis (September 

 14 and 16, 1854), I cannot call to mind that I ever saw 

 coruscations or waves of electric light at all approaching 

 those seen at Christiania on this occasion. The books 

 say comparatively little about these coruscations, nor do 

 the letters in Nature, vol. xxii. p. 361, mention them as 

 seen in England. Vet they probably represent the most 

 important part of the phenomenon, the active discharge of 

 electric energy. 



I neither saw nor heard anything in Norway of an 

 aurora on the night of August 1 1. About the dates I give 

 there can be no possible mistake, because the steamboat 

 from Christiania to Hull departed as usual on Friday 

 evening (August 13). The times mentioned are the local 

 times by the public clock at the Christiania University 

 Buildings. W. Stanley Jevons 



P.S. — The above account was mostly written a few 

 days after my return to London, according to notes taken 

 at the time. I print it now for what it may be worth. 

 After thinking the matter over for three months, and 

 comparing tlie auroral coruscations above described with 

 the exquisite discoveries of Mr. Crookes, taking into 

 account also some remarks in the article on auroras in 

 the new edition of the " Encyclopasdia Britannica," I 

 venture to make the suggestion that these corusca- 

 tions arise from highly tenuous matter (in what Mr. 

 Crookes calls the radiant state) projected through the 

 higher parts of the atmosphere. It is not possible 

 by words to give an impression of such a phenomenon 

 in the least degree approaching to that naturally acquired 

 by watching it under favourable circumstances for several 

 hours. My belief is, that during the auroras described, 

 puffs, as it were, of radiant matter were discharged at 

 a great elevation above the earth's surface, and the 

 luminosity of these puffs perhaps arises from conflicts 

 between the projected molecules and those already spread 

 about the almost vacuous space. The arch and most of 

 the streamers probably belong to a lower, though still a 

 very high part of the earth's atmosphere, but certain of 

 the streamers, as well as patches of luminous matter seen 

 on the night of the 13th, certainly exist in the lofty regions 

 through which the ladiant matter is projected. The ex- 

 planation of the streamers must probably be approached 

 through that of the coruscations, but they are effects of a 

 very different kind. W. S. J. 



November 22 



THE INFLUENCE OF A TUNING-FORK ON 

 THE GARDEN SPIDER 



HAVING made some observations on the garden 

 spider which are I believe new, I send a short 

 account of them in the hope that they may be of interest 

 to the readers of Nature. 



Last autumn, while watching some spiders spinning 

 their beiutiful geometrical webs, it occurred to me to try 

 what effect a tuning-fork would have upon them. On 

 sounding an A fork and lightly touching with it any leaf 

 or other support of the web or any portion of the web 

 itself, 1 found that the spider, if at the centre of the web, 

 rapidly slews round so as to face the direction of the fork, 

 feeling with its fore feet along which radial thread the 

 vibratton travels. Having become satisfied on this point, 

 it next darts along that thread till it reaches either the 

 fork itself or a junction of two or more threads, the right 

 one of which it instantly determines as before. If the 

 fork is not removed when the spider has arrived it seems 

 to have the same charm as any fly : for the spider seizes 

 it, embraces it, and runs about on the legs of the fork 

 as often as it is made to sound, never seeming to learn 



