A. MATHEMATICS AND ASTRONOMY. 47 



ion. At the appearance of this comet in February, March, 

 and April, 1875, Bredichin, at Moscow, and Struve, at Poul- 

 kova, were successful in making observations which are best 

 accounted for by assuming an acceleration since 1871 of 

 about two thirds as much as that indicated at previous ap- 

 paritions, as though the physical changes in the interior of 

 the comet which occurred in 1868 had affected not only its 

 movements at that time, but also, in a lesser degree, are con- 

 tinued to the present time. 



OX COMETARY ORBITS. 



In giving a general review of the statistics relative to the 

 orbits of comets, Guillemin states that 177 have parabolic 

 orbits, 73 elliptic, and 14 hyperbolic. To these must be 

 added a large number of other comets not yet accurately 

 computed, so that we may calculate that of these bodies 

 scarcely one sixth are foreign to the solar system, and the 

 remainder circulating about the sun as do the planets. 

 With regard to the inclinations of their orbits to the orbit 

 of the earth, he shows that the greater inclinations are more 

 frequent than the lesser; so that the comets whose paths 

 are confined to the zodiac form scarcely a quarter of those 

 that are known. As regards the direction in which they 

 move in their orbits about the sun, the direct and the ret- 

 rograde motions are about equally divided. But if we ex- 

 amine in detail the three classes the parabolic, the elliptic, 

 and the hyperbolic orbits we find that among the elliptic 

 orbits the direct motions are twice as numerous as the ret- 

 rograde. As regards the distance to which they approach 

 the sun, 192 have come between the earth and the sun, and 

 66 between the earth and Jupiter ; while between the orbits 

 of Venus and Mars not less than 130 of these have passed. 

 Bulletin Hebdom. Association Scientifique, 1875, 262. 



OX THE STRUCTURE OF COMETS AXD METEORS. 



From an examination of the gases occluded in the Iowa 

 meteorite of February 12, 1875, Professor Wright, of New 

 Haven, concludes that his results have an important bear- 

 ing upon the theory of comets and their tails, warranting 

 the following conclusions: First, the stony meteorites are 

 distinguished from the iron ones by having the oxides of 



