318 Mr. J. Rand Capron on the Auroral 



A second unknown resistance may now be substituted and 

 measured as before, simply by altering the resistance of R, 

 with the certainty that when there is a balance the current 

 is of the same strength as in the former case. The resistance 

 nx remains unchanged throughout. It is of course necessary 

 so to choose the values of a, n, and E that x may be greater 

 than the resistance to be measured ; and it is generally de- 

 sirable that the resistance of the whole bridge should be made 

 as high as conveniently possible. 



The great advantage of this method over others that suggest 

 themselves lies in the fact that, since it is never necessary to 

 close the circuit for more than a moment, the electromotive 

 force and resistance of the battery remain sensibly constant 

 during a long course of experiments. 



XL VII. The Auroral Beam of November 17, 1882. 



By J. Rand Capron, F.R.A.S., F.M.S.* 



[Plate VII.] 



nVTOVEMBER last (1882) was remarkable for the great 

 -i-^l auroral storm, or, rather, series of storms, which prevailed 

 over a considerable portion of the globe during the latter half 

 of that month. 



Accounts of brilliant displays from the Shetland Islands, at 

 Edinburgh, a great number of localities in England, Rome, 

 and Florence soon made their appearance in the public prints; 

 and to these later on were added others from America, Cali- 

 fornia, Spain, Sweden, Belgium, the Netherlands, and other 

 countries. 



Continuous aurorge were seen at Trondhjem from the 12th 

 to the 18th of the month ; and I traced almost incessant dis- 

 plays in these latitudes from the 13th to the 24th at least — the 

 motions of the telegraph-needles acquainting us that aurora 

 were not only present when actually visible, but by day and 

 during clouded nights. 



Also accompanying these were considerable groups of solar 

 spots, one the largest ever seen at Greenwich, and a wide- 

 spread disturbance by earth-currents of State telegraphic 

 communication in nearly all the countries above mentioned. 

 It was during one of these storms that, in the south of England 

 and the adjacent parts of France and Belgium, a phenomenon 

 was seen which, though apparently not without precedent in 

 the annals of aurorae, was at least of a rare and striking 

 character. 



* Communicated by the Author. 



