HUBERT ANSON NEWTON. 



273 



The mean foreshortening of paths. 



The mean length of the visible part of the real paths. 



The mean time of flight as estimated by observers. 



The distribution of the orbits of meteoroids in the solar system. 



The daily number of shooting stars, and the density of the 

 meteoroides in the space which the earth traverses. 



The average number of shooting stars which enter the atmosphere 

 daily, and which are large enough to be visible to the naked eye, 

 if the sun, moon and clouds would permit it, is more than seven 

 and a half millions. Certain observations with instruments seem 

 to indicate that this number should be increased to more than 

 four hundred millions, to include telescopic shooting stars, and there 

 is no reason to doubt that an increase of optical power beyond that 

 employed in these observations would reveal still larger numbers of 

 these small bodies. In each volume of the size of the earth, of the 

 space which the earth is traversing in its orbit about the sun, there 

 are as many as thirteen thousand small bodies, each of which is 

 such as would furnish a shooting star visible under favorable 

 circumstances to the naked eye. 



These conclusions are certainly of a startling character, but not of 

 greater interest than those relating to the velocity of meteoroids. 

 There are two velocities to be considered, which are evidently con- 

 nected, the velocity relative to the earth, and the velocity of the 

 meteoroids in the solar system. To the latter, great interest attaches 

 from the fact that it determines the nature of the orbit of the 

 meteoroid. A velocity equal to that of the earth, indicates an orbit 

 like that of the earth; a velocity ^/2 times as great, a parabolic 

 orbit like that of most comets, while a velocity greater than this 

 indicates a hyperbolic orbit. 



Professor Newton sought to form an estimate of this critical 



o 



quantity in more than one way. That on which he placed most 

 reliance was based on a comparison of the numbers of shooting stars 

 seen in the different hours of the night. It is evident that in the 

 morning, when we are in front of the earth in its motion about the 

 sun, we should see more shooting stars than in the evening, when we 

 are behind the earth ; but the greater the velocity of the meteoroids 

 compared with that of the earth, the less the difference would be in 

 the numbers of evening and morning stars.* 



* It may not be out of place to notice here an erratum which occurs both in the 

 Memoirs of the National Academy and in the abstract in the American Journal of 

 Science, and which the writer finds marked in a private copy of Professor Newton's. 

 In the table on p. 20 of the memoir and 206 of the abstract, the column of numbers 

 under the head "hour of the night" should be inverted. There is another displace- 

 ment in the table in the memoir, which is, however, corrected in the abstract. 

 G. II. S 



