A CATALOGUE OF OBSERVATIONS OF LUMINOUS METEORS. 41] 
apex of the earth’s way are only 38° and 10° respectively, yet other circum- 
apical meteoric streams may give rise to aérolitic falls. The annual varia- 
tion of frequency of aérolites is not nearly so marked as the corresponding 
law of their diurnal variation * ; and this would actually be the case, if the 
materials of a few meteor-currents near the apex should, occasionally, produce 
aérolitic falls, 
The sixth chapter contains some propositions relative to the effects of the 
earth’s motion, and of its attraction, during its appulse with meteoric currents. 
Supposing D to be the real density or number of meteors per minute of a 
shower of shooting-stars which would fall on a single horizon exposed ver- 
tically to it were the carth at rest, z the apparent zenith-distance, and ¢ the 
apparent elongation of the radiant-point of the shower from the apex of the 
earth’s way, then, considering the real velocity of meteors to be that of 
bodies moving in parabolic orbits, and t6 be unaffected by the earth’s attrac- 
tion, the apparent density d, or the number of meteors actually observed per 
minute, is given by the formula 
d=D cos z/3+ WV 2 cose, 
and will generally depend on the apparent angular distance of the radiant- 
point from the zenith of the observer, and from the apex of the earth’s way. 
The frequency of the meteors will be greatest when the radiant-point coin- 
cides with the apex of the earth’s way, and when both points are in the 
observer’s zenith}. Applying the formula to calculate the real density of 
the meteors in the great shower of the 13th and 14th of November 1866, 
from the apparent density (123 meteors per minute) as observed at Green- 
wich, making z=65°, e=10°, the value of D, or the real density of the 
stream for the observers of the shower at Greenwich, is found to be 171 
meteors per minute. The effect of the earth’s motion through the swarm, in 
increasing the frequency of the meteors, was thus much more than counter- 
balanced by the low position of the radiant-point, tending to reduce their 
_ apparent number. Had the latter point been in the zenith, the number of 
meteors recorded in a minute would have been 291, instead of 123, as ob- 
_ served, and would greatly have increased the splendour of the display. 
The effect of the earth’s attraction cannot always be neglected, as it de- 
flects the parallel courses of the meteors into hyperbolic curves, And those 
meteors are most deflected which just graze the earth’s atmosphere, and 
which overtake it with the slowest speed from the direction of the anti-apex ; 
_ the total deflection in this case, on leaving the sphere of the earth’s attrac- 
tion, is 34° 40’ ; meteors so diverted from their original course become truly 
_ sporadic, and their radiant-region must speedily grow diffuse; but in the 
case of a meteor-current arriving from the direction of the apex, the total 
_ deyiation cannot exceed 1° 24': while for meteor-currents having their 
apparent points of divergence midway between these points, or situated 90° 
_ from the apex, the greatest possible deviation is 7°56’. As the meteors of 
the 13th-14th of November diverge nearly from the apex of the earth’s 
way, and a second deflection of the same meteors to the utmost extent of 
1° 28' is very unlikely to take place, the great accuracy of divergence of the 
meteors of this shower from a well-defined radiant-point is readily explained. 
__ * See the Table in the above Report for 1860, p. 116. 
__ t For in that case cose=cos z=1. ; 
_ } See an important article by Prof. Twining in reference to the influence of the earth’s 
_ attraction on “'The August Meteors,” in the American Journal of Science for November 
1861, vol. xxxii. 
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