140 
rOPULAE SCIE>"CE EEVIEW. 
in reality the astronomers j list named had no other grounds for 
their anticipations than first the fact that Biela’s comet was 
known to have recently passed the descending node of its orbit 
(or the place where it passes nearest to the earth’s orbit), and 
secondly their confidence in the theory that meteors and comets 
are in some way associated. A prediction such as this became 
therefore in some sense a crucial test of this theory — not indeed 
that the failure of the prediction would have disproved the 
theory (because negative evidence counts for little in this 
matter), but that its fulfilment would supply the only form of 
positive evidence yet wanting to that theory. 
I do not here enter at length on the remarkable circum- 
stances connected with Biela’s comet, because they have been 
elsewhere stated at considerable length, and are probably known 
to the majority of those who will read these lines. Let it suffice 
to say that the comet was one of short period, returning at 
mean intervals of 6*635 years ; that in 1837 it was observed to 
be divided into two distinct comets ; that it returned in 1852, 
and both the comets were then still in existence ; that whether 
it returned (unchanged in general aspect) in 1858-59 or not, is 
unknown, because its calculated course was such as to render 
observation impossible ; and lastly that in 1866, and again last 
year, it was searched for in vain with telescopes of great 
power. 
Now it crossed the earth’s path last year nearly twelve weeks 
before November 27, when the earth herself traversed the 
place at which the comet crosses her orbit. And since the 
meteors of November 13-14 have been seen, not merely a few 
months, but several years after the nodal passage of their comet, 
it seemed not unreasonable to expect a considerable meteoric 
display on or about November 27. The exact date was not 
indeed very accurately determined, and the reason is readily 
seen. I invite the reader’s special attention to the point, 
because it has been somewhat singularly overlooked even by 
astronomers of great mathematical attainments. The comet 
itself had its place of passage readily calculated, and it might 
seem at first sight that whenever the earth came to that place 
the display should occur. But manifestly the position of the 
cometic orbit for November 27, when the earth crossed that 
orbit’s node, would not be identical with the position of that 
orbit three months or so before, when the comet passed its 
node. It might then seem that this latter position was what 
astronomers should calculate, and as a matter of fact this is 
what was commonly done. We find the position of the node 
of the orbit for the end of November assigned as the place 
where the encounter of the earth with the meteoric flight was 
to take place. But this view is as incorrect as the former. 
