40 RECORD OF AURORAL PHENOMENA. 



all the same direction, were made to cross the magnetic meridian nearly at right angles. The 

 apparent convergence of such masses of cloud towards opposite points of the horizon, which has 

 been frequently noticed by meteorologists, is, of course, an optical deception, produced when 

 they lie in a plane parallel to that on which the observer stands. 



These circumstances are here noticed, because if it should be hereafter proved that the Aurora 

 depends upon the existence of certain clouds, its apparent polarity ma)', perhaps with more 

 propriety, be ascribed to the clouds themselves which emit the light; or, in other words, the 

 clouds may assume their peculiar arrangement through the operation of one cause (magnetism 

 for instance), while the emission of light may be produced by another, a change in their internal 

 constitution perhaps, connected with a motion of the electrical fluid. These crude opinions are 

 offered with diffidence, and my knowledge on these subjects is so limited, that I attach no 

 importance to them; but it appears to me that they would be strengthened were the attempts 

 now making to excite magnetism, by the electrical or galvanic fluid, to prove successful. 



Generally speaking, the Aurora appeared in small detached masses for some time before it assumed 

 that couvergency towards opposite parts of the horizon which produced the arched form. An 

 observation that I would connect with the previous remarks, by saying that it was necessary 

 for the electric fluid (or the Aurora, if they are the same) to operate for some time before the 

 polarity of the thin clouds in which it has its seat is produced. 



This part of the subject, however, is more intimately connected with the interesting observations 

 made on the variation of the magnetic needle by Captain Franklin and Mr. Hood. The object 

 of my notes was merely to record the optical appearances of the meteor. 



An electrometer, constructed upon Saussure's plan, placed in an elevated situation out of doors, 

 exhibited no signs of a change from the atmosphere at any time during the winter. The elec- 

 tricity of our bodies, however, at times was so great, that the pith balls instantly separated to 

 their full extent upon approaching the hand to the instrument, and our skins were, in the middle 

 of winter, so dry that rubbing the hands together considerably increased their electricity, and, 

 at the same time, produced a smell similar to that which is often perceived when the cushion of 

 an electrifying machine rubs hard against the cylinder. 



The same thing was observed more sensibly in some stuffed quadrupeds that hung in our apart- 

 ments. Their furred skins, whether rubbed or not, often accumulated such a charge of the 

 electrical fluid, that, when the knuckles were presented to them, they gave a smart shock, which 

 was felt as far as the elbow. 



The Aurora did not often appear immediately after sunset. It seemed that tlie absence of that lumi- 

 nary for some hours was in general required for the production of a state of atmosphere favorable 

 to the generation of the Aurora. On one occasion only (March 8, 1821), did I observe it dis- 

 tinctly previous to the disappearance of daylight. 



By the way of more perfectly describing one form of the Aurora, rather than with a view of draw- 

 ing any inference, I shall state that the slender beams of light which compose the Aurora when 

 its motions are rapid, are exactly similar to what would be produced by a quick succession of 

 electric sparks, elicited from a charged cylinder by a body, studded with a row of points, moved 

 rapidly to and fro before it. 



Or, supposing a long range of cloud were to commence at one end to impart, from successive 

 points of its surface, its charge to a similar parallel mass, a current of light would be produced, 

 apparently consisting of parallel beams, lying at right angles to its line of direction, as described 

 on the night of the 29th-30th December at 2k. a. m. 



Were the clouds supposed to lie in different planes, and to be bounded by curved edges, every 

 variety of form which that species of Aurora assumes might be produced. 



The color of the light of the Aurora is not always noted in the following pages, but, when faint, 

 it was generally steel-gray or that of the galaxy. 



When the low hazy modification of cirro-stratus appeared in the sky, the light, for the most 

 part, was a gold-yellow color, more or less deep ; and wheu the sky was clear, or when only a 

 few fine threads or thin shoots of cloud were visible, the colors were vivid and prismatic. 



I have never heard any sound that could be unequivocally considered as originating iu the Aurora; 



