HUBERT ANSON NEWTON. 2*79 



place was then 75,000. This gives a density of the meteoroids in 

 space represented by one to a cube of twenty miles edge. Three 

 hours later the frequency had fallen to one-tenth of the maximum 

 value. The really dense portion of the stream through which we 

 passed was less than 100,000 miles in thickness, and nearly all would 

 be included in a thickness of 200,000 miles. 



A formula is given to express the effect of the earth's attraction 

 on the approaching meteoroids in altering the position of the radiant. 

 This is technically known as the zenithal attraction, and is quite 

 important in the case of these meteors on account of their small 

 relative velocity. The significance of the formula may be roughly 

 expressed by saying that the earth's attraction changes the radiant of 

 the Biela meteors, toward the vertical of the observer, one-tenth of 

 the observed zenith distance of the radiant, or more briefly, that the 

 zenithal attraction for these meteors is one-tenth of the observed 

 zenith distance. The radiant even after the correction for zenithal 

 attraction, and another for the rotation of the earth on its axis, is not 

 a point but an area of several degrees diameter. The same has been 

 observed in regard to other showers, but the result comes out more 

 distinctly in the present case because the meteors were so numerous 

 and the shower so carefully observed. 



This implies a want of parallelism in the paths of the meteors, and 

 it is a very important question whether it exists before the meteoroids 

 enter our atmosphere, or whether it is due to the action of the 

 atmosphere. 



Professor Newton shows that it is difficult to account for so large 

 a difference in the original motions of the meteoroids, and thinks it 

 reasonable to attribute a large part of the want of parallelism to the 

 action of the atmosphere on bodies of an irregular form, such as we 

 have every reason to believe that the meteoroids have, when they 

 enter our atmosphere. The effect of the heat generated will be to 

 round off the edges and prominent parts, and to reduce the meteor 

 to a form more and more spherical. It is, therefore, quite natural 

 that the greater portion of the curvature of the paths should be 

 in the invisible portion and thus escape our notice. It is only in 

 exceptional cases that the visible path is notably curved. 



But the great interest of the paper centers in his discussion of the 

 relation of this shower to preceding showers, and to the orbit of 

 Biela's comet. The changes in the date of the shower (from Dec. 6 

 to Nov. 27) and in the position of the radiant are shown to be related 

 to the great perturbations of Biela's comet in 1794, 1831, and 1841-2. 

 The showers observed by Brandes, Dec. 6th, 1798, by Herrick, Dec. 7th, 

 1838, and by Heis, Dec. 8th and 10th, 1847, are related to the orbit 

 of Biela's comet as it was in 1772; while the great showers of 1872 



