236 Intelligence and Miscellaneous Articles. 



corresponding increase in the number of aerolites, which cannot be 

 wholly accounted for by the increased number of observers. Now 

 there are two obvious methods by which these variations may be ex- 

 plained. Either (1) the orbits of the meteoric rings which intersect 

 the earth's path were so changed by perturbation towards the close 

 of the twelfth century as to prevent the appulse of the meteoric 

 groups with the earth's atmosphere, or (2) the nebulous matter is very 

 unequally diffused through the sidereal spaces. That the former has 

 not been the principal cause is rendered extremely probable by 

 the fact that the number of epochs of periodical showers was no 

 greater during the cycle of abundance than in that of paucity. We 

 conclude, therefore, that during the interval from 700 to 1200 the 

 solar system was passing through, or near, a meteoric cloud of very 

 great extent, that from 1200 to 1700 it was traversing a region 

 comparatively destitute of such matter, and that about the com- 

 mencement of the eighteenth century it again entered a similar ne- 

 bula of unknown extent. 



The fact that the August meteors, which have been so often sub- 

 sequently observed, were first noticed in 811 renders it probable that 

 the cluster was introduced into the planetary system not long pre- 

 viously to the year 800. It may be also worthy of remark that the 

 elements of the comet of a.d. 770 are not very different from those 

 of the August meteors and the third comet of 1862*. 



Adopting Struve's estimate of the sun's orbital velocity, we find 

 the diameter of the nebula traversed in 500 years to be fourteen 

 times that of Neptune's orbit. 



It is remarkable that, with the exception of Mars, the perihelia of 

 the orbits of all the principal planets fall in the same semicircle of 

 longitude — a fact which can hardly be regarded as accidental. Now, 

 if the orbits were originally circular, the motion of the solar system 

 through a nebulous mass not of uniform density would have the ob- 

 vious effect of compelling the planets to deviate from their primitive 

 orbits and move in ellipses of various eccentricities. It is easy to 

 perceive, moreover, that the original perihelion points of all the or- 

 bits would be on that side of the system which had passed through 

 the rarer portion of the nebulous mass. We have thus a possible 

 cause of the eccentricity of the planetary orbits, as well as of the 

 observed distribution of their periheliaf. 



4. The particles of a cometic mass, being at unequal distances 

 from the sun, will tend to move at different rates and in somewhat 

 different orbits. This tendency will gradually overcome the feeble 



* The interval between the perihelion passage of 770 and that of 1862 

 is equal to nine periods of 121*36 years. Oppolzer's determination of the 

 period of 1862 III. is 1215 years. Hind remarks that the elements of the 

 comet of 770 are " rather uncertain," but says "that the general character 

 of the orbit is decided." It may be worthy of remark that a great me- 

 teoric shower, the exact date of which has not been preserved, occurred 

 in 770. 



t This suggestion is clue to R. A. Proctor, F.R.A.S., the distinguished 

 author of ' Saturn and its System.' 



