Americayi Association, 251 



pheric excitations ; secondly, from their occurring at the same hour 

 of the night in places very far distant from each other ; thirdly, 

 from the velocity of their motions ; and fourthly from the perio- 

 dicity of their occurrence during a certain time, and then disap- 

 pearing altogether from the heavens. With regard to their hav- 

 ing a revolution round the sun, he thought tliat to be affected by 

 the question of zodiacal light, with which he thought they had 

 some connection ; and if it should appear that the Zodiacal Light 

 was a ring round the earth it would not affect this conclusion. 

 He had previously stated that the long series of brillant Auroras 

 which bad been recently witnessed would soon be over and not 

 appear again until after a period of about forty years ; the regu- 

 lar period being calculated at sixty years. He would ask mem- 

 bers of the Association to remark that for jfive or six years 

 past the brilliancy of the Aurora had diminished, and he would 

 ask those who could not look back to ISSY and 1840 when the 

 maximum brightness of the Aurora was observed, not to consider 

 the appearances now seen as comparable to those exhibitions which, 

 the older members could remember. He would ask tbem only to 

 consider as the Aurora those immense banks of light which, in 

 1835 and 1837 used to appear in the North West, rising into 

 columns of a scarlet or blood-red colour, with spindles moving to 

 the South East, and arranging themselves in a magniiicent crown 

 round the zenith ; while the whole heavens were suffused with 

 crimson light. For ffve or six years no such exhibition had oc- 

 curred. In 1840 there were 75 strikingly magnificent exhibi- 

 tions of the Aurora, while for several years they had scarcely 

 seen one. After the discovery of the analogy between electricity 

 and lightning, it became the practice to ascribe everything to 

 electricity. No one could doubt that electricity holds a high place 

 among the ultimate causes of natural phenomena ; he only object- 

 ed, to ascribing everything to that agency without even first 

 proving its presence. This practice had damped enquiry into 

 many phenomena, and among others, into those relating to the 

 Aurora Borealis, and it was always deemed sufiicient to say that 

 the Aurora was an electrical phenomena. Various arguments were 

 urged in favour of the electrical hypothesis, and upon them he 

 would remark that the resemblances between electricity and the 

 Aurora had been greatly overstated. Fire, the sun, a lamp, or a 

 star have all some resemblance to the Aurora, but from his own 

 observation he vras compelled to say that the likeness v/as very 



