CONSTITUTION AND MOVEMENTS OF COMETS. 259 



quantity of atoms is small, and therefore the force of mu- 

 tual gravitation small, there will be nothing to coerce the 

 atoms into union. Whence we infer that these detached 

 fragments of nebulous matter will continue in their origi- 

 nal state. We find that they do so. Comets consist of an 

 extremely rare medium, which, as shown by the descrip 

 tion already quoted from Sir John Herschel, has charac 

 ters like those we concluded would belong to partially- 

 condensed nebulous matter. 



Yet another very significant fact is seen in the distribu- 

 tion of comets. Though they come from all parts of the 

 heavens, they by no means come in equal abundance from 

 all parts of the heavens ; but are far more numerous about 

 the poles of the ecliptic than about its plane. Speaking 

 generally, comets having orbit-planes that are highly in- 

 clined to the ecliptic, are comets having orbits of which the 

 major axes are highly inclined to the ecliptic — comets that 

 come from high latitudes. This is not a necessary connex- 

 ion ; for the planes of the orbits might be highly inchned 

 to the ecliptic while the major axes were inclined to it very 

 little. But in the absence of any habitually-observed rela- 

 tion of this kind, it may safely be concluded that, on the 

 average^ highly-inclined cometary orbits are cometary or- 

 bits with highly-inclined major axes ; and that thus, a pre- 

 dominance of cometary orbits cutting the plane of the 

 ecliptic at great angles, imphes a predominance of comet- 

 ary orbits having major axes that cut the ecliptic at great 

 angles. Now the predominance of highly inclined com- 

 etary orbits, may be gathered from the following table, 

 compiled by M. Arago, to which we have added a column 

 giving the results up to a date two years later. 



