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POPULAR SCIENCE REVIEW. 
compensatory effects — the comets and the bodies travelling 
twelve weeks behind being in the course of many years sub- 
jected to every variety of perturbative effect in the same 
respective proportions — yet such cycles of compensation are 
enormously long in the case of bodies moving in an orbit like 
that of Biela’s comet ; and practically it may be said that 
compensation is never effected.* 
So that unless calculations could be made of the perturba- 
tions affecting those meteors themselves which are travelling 
twelve weeks behind the comet, we could not possibly be certain 
as to the place where the earth would actually encounter 
the meteor flight, or whether such an encounter would take 
place at all. The calculation would be one of immense diffi- 
culty, even if we knew where and how the meteors had been 
moving at some particular date ; but as we know nothing on 
either point, it is simply impossible to enter upon the calcu- 
lation. 
It will presently be seen that these considerations bear 
importantly on the opinion we are to form respecting the events 
which have recently occurred. 
It is in the knowledge of all our readers that on November 
27th last, the anticipated display of meteors did actually occur. 
It was a display very remarkable in character. The meteors 
were even more numerous, in fact they were far more numerous 
than during the memorable shower of the night between 
November 13-14, 1866 ; though the meteors were not so large 
on the average as those seen on the latter occasion. I select 
from among many accounts the excellent description given by 
Professor Grrant, because his skill and practice as an observer gives 
* One may reason thus : Given a body travelling in the orbit of Biela's 
comet then the orbit of this body will pass through endless changes. Its 
eccentricity will wax and wane ; its inclination will increase and diminish ; 
its line of apsides will advance and regrede, advancing on the whole j its 
line of modes will advance and regrede, regreding on the whole ; and count- 
less ages must elapse before its orbit resumes its original figure, for the four 
kinds of change will not have synchronous periods. Now the same is true 
of another body, having at the beginning the same orbit but twelve weeks 
in front or behind. This body will have its orbit passing through endless 
changes, and will only after countless ages be found travelling in the same 
orbit as at first. But the period in which this will happen is not the same 
period in which the former will happen. Each period is enormously long ; 
but after the lapse of either the bodies are not travelling in the same orbit. 
When one period has elapsed, the other is far from being completed ; when 
the latter is completed, the former is far past. Nor does it follow that the 
perturbing planets are in the same position as when the changes began. 
Many thousands of such periods must pass for both bodies before there is a 
near approach to the original state of things in all respects. 
