598 



APPENDIX. 



[No. III. 



I think I have on some occasions discerned a polarity in the masses of 

 cloud belonging to a certain kind of cirro-stratus, which approaches to cirrus, 

 by which their long diameters, having all the same direction, were made to 

 cross the magnetic meridian nearly at right angles. The apparent conver- 

 gence of such masses of cloud towards opposite points of the horizon, which 

 has been frequently noticed by meteorologists, is of course an optical decep- 

 tion, 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 here- 

 after proved that the Aurora depends upon the existence of certain clouds, its 

 apparent polarity may, 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 electri- 

 cal 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 convergency 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 charge from the atmosphere at any 

 time during the winter. The electricity of our bodies, however, at times was so 

 great, that the pith balls instantly separated to their full extent upon approach- 

 ing 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 



