M^fo*J&*fc 



THE 



AMERICAN JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



Akt. LI. — On the effect upon the earth's velocity produced by small 

 bodies passing near the earth ; by H. A. Newton. 



1. The space through which the earth travels is traversed 

 also by small bodies, or meteoroids. These give meteors of all 

 degrees of brilliancy, and it is reasonable to assume that 

 bodies too small to furnish visible meteors also lie along our 

 path. The impact of these bodies upon the earth, and the con- 

 sequent increase of the earth's mass, have their effect upon the 

 earth's motions both of rotation and revolution, and hence 

 upon the lengths of the year and the day. The moon's orbit 

 and the length of the month likewise suffer change. 



Professor Oppolzer in a paper in the Astronomische Nach- 

 richten (No. 2573) has considered the amount of these two 

 actions and has computed the density which the rneteoroid 

 matter must have in the space which the earth is traversing 

 in order to produce upon the relative lengths of the month 

 and the day the observed and unexplained acceleration of 

 the moon's mean motion. This computed density is 59x10" 18 , 

 the mean density of the earth being unity, and is at least a 

 myriad times, perhaps a million times as great as can be 

 reasonably assigned to observed meteors.* But a body that 

 passes near to the earth has also an action of like character 

 by reason of the attraction of gravitation alone, and I pro- 

 pose to show its amount, for it seems well worth showing 

 that the bodies which pass near us do not have an effect at 

 all comparable with that produced by those which actually 

 come into the earth's atmosphere. 



* A proper amount of cosmic dust, if we can reasonably assume that so large 

 an amount of this questionable substance exists, might explain that acceleration. 

 Air. Jour. Scl— Third Series, Vol. XXX, No. 180.— Dec, 1885. 

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