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POPULAR SCIENCE REVIEW. 
treated in a totally different manner. He assumes the period 
(or which amounts to the same thing, the major axis) of the 
object’s orbit to be the same as that of Biela’s comet, and that 
the object was moving from the earth in the interval between 
December 2 and 3, deducing elements nearly resembling those 
of Biela’s comet. 
It appears to me that the discordances obtained by different 
astronomers depend largely on the assumption that the object 
seen by Pogson, if identifiable at all with Biela’s meteor-train, 
must in a special manner be identified with the cloud of 
meteors through which the earth passed on the night of 
November 27. But is there any valid reason for this assump- 
tion ? It may seem at first sight that there is ; that a cloud 
of meteors sufficiently dense to produce so remarkable a display 
should be visible, when it had passed beyond the earth, as a 
cloud of light in the telescopic field. But if we consider the 
real distribution of those meteors in space, we shall find reason 
to conclude that they were far too sparsely distributed to be 
visible under any circumstances, by the light they were capable 
of reflecting. Let it be remembered that the display lasted about 
six hours, and that during that period about 50,000 meteors at the 
utmost appeared above the horizon of any given place. But let 
us set 100,000 as the number of meteors so appearing, and the 
time at only four hours. Now the region of meteor-traversed 
atmosphere above the horizon plane of any station may be 
taken as a plano-convex lens, its plane circular face having a dia- 
meter certainly not less than 1,000 miles ; and as the radiant was 
high above the horizon, we shall be within the truth in con- 
cluding that such a plane on the average presented (as supposed 
to be seen from the advancing meteors) an area equalling the 
100th part of the area presented by the whole disk of the 
earth. So that if we take 10,000,000 for the total number of 
meteors falling on the earth during four hours, we shall cer- 
tainly not underestimate the number (referring always to 
meteors large enough to become visible to the naked eye). 
Now, the actual region of space traversed by the earth in four 
hours is a cylinder 260,000 miles long and having a cross 
section nearly 8,000 miles in diameter. Such a cylinder would 
have a volume of 12,500,000,000,000 cubic miles, and to each 
meteor of the 10,000,000 there would therefore correspond an 
average space of 1,250,000 cubic miles ; that is, a space corre- 
sponding to a cube nearly 108 miles in length and breadth and 
height. Since such meteors as were seen on the night of 
November 27 have been estimated at less than an ounce in 
weight (in many cases only a few grains), it follows that their 
dimensions are inconsiderable. The largest can scarcely, when 
solid, be an inch in diameter. It will be conceived, therefore, 
