COMETS. 23 



have a slow lateral motion from east to west. These sudden flashes of auroral 

 light are known by the name of the "Merry Dancers," and form an important 

 feature of nearly every splendid aurora. 



The color of the aurora is very variable. If the aurora be faint its light is 

 usually white, or a pale yellow. When the aurora is brilliant, the sky exhibits at 

 the same time a great variety of tints ; some portions of the sky are nearly white, 

 but with a tinge of emerald green; other portions are of a pale yellow or straw 

 color; others are tinged with a rosy hue, while others have a crimson hue, which 

 sometimes, but rarely, deepens to a blood red. These colors are ever varying in 

 position and intensity. 



There was another display on Thursday morning ult., lasting from after mid- 

 night until daybreak, with recurring fits of activity, but not so brilliant or extend- 

 ing over so much of the heavens as that of Sunday night. Although somewhat 

 similar, with the exception that the phenomenon of the "Merry Dancers" did not 

 occur during the display. 



A remarkable and very rare phenomenon occurred during this display, viz : 

 The sky became obscured and a light shower of rain fell from 1:35 ^- ^^- ^^ '"45 

 A. M., shortly afterwards the sky became clear, and disclosed auroral activity 

 simi ar to that of Sunday night, but not extending to so high an altitude. The 

 highest beams did not reach above 60°, nor were the colors as brilliant or so well 

 defined. 



COMETS. 



R. J. m'caRTY, KANSAS CITY, MO. 



Such is the magnificent aspect of comets, such their shape, so remarkable 

 the contrast ^between them and the surrounding stars, so capricious do they seem 

 in their movements, so seldom do they appear and so quickly do they vanish, 

 that it is by no means strange that their appearance should fill the ignorant with 

 alarm and the wise with admiration and curiosity. 



Previous to the apparition of the celebrated comet of i68d, we may say 

 nothing was known of the motions of these extraordinary bodies, except that they 

 had been observed to make their appearance among the stars, approach the sun 

 for a certain time, and then recede until lost in the depths of space. 



In elaborating the principle of gravitation. Sir Isaac Newton had demon- 

 strated that any body revolving about the sun under the dominion of that princi- 

 ple must describe some one of the conic sections, with the sun at its focus, and 

 that the particular conic described would be determined solely by the velocity of 

 the body at any given point of its orbit. I have here a cone so cut as to show 

 the curves alluded to. 



A body moving with a velocity equal to that which it would acquire by fall- 

 ing directly to the center of the sun (supposing the attraction of the sun for the 



