ould ever become as eccentric as
that of the planet Juno or Pallas, a great change of climate might be
conceived to result, the winter and summer temperatures being sometimes
mitigated, and at others exaggerated, in the same latitudes.

It is much to be desired that the calculations alluded to were executed,
as even if they should demonstrate, as M. Arago thinks highly
probable,[206] that the mean amount of solar radiation can never be
materially affected by irregularities in the earth's motion, it would
still be satisfactory to ascertain the point. Such inquiries, however,
can never supersede the necessity of investigating the consequences of
the varying position of continents, shifted as we know them to have been
during successive epochs, from one part of the globe to the other.

Another astronomical hypothesis respecting the possible cause of secular
variations in climate, has been proposed by a distinguished
mathematician and philosopher, M. Poisson. He begins by assuming, 1st,
that the sun and our planetary system are not stationary, but carried
onward by a common movement through space; 2dly, that every point in
space receives heat as well as light from innumerable stars surrounding
it on all sides, so that if a right line of indefinite length be
produced in any direction from such a point, it must encounter a star
either visible or invisible to us. 3dly, He then goes on to assume, that
the different regions of space, which in the course of millions of years
are traversed by our system, must be of very unequal temperature,
inasmuch as some of them must receive a greater, others a less, quantity
of radiant heat from the great stellary inclosure. If the earth, he
continues, or any other large body, pass from a hotter to a colder
region, it would not readily lose in the second all the heat which it
has imbibed in the first region, but retain a temperature increasing
downwards from the surface, as in the actual condition of our
planet.[207]

Now the opinion originally suggested by Sir W. Herschel, that our sun
and its attendant planets were all moving onward through space, in the
direction of the constellation Hercules, is very generally thought by
eminent astronomers to be confirmed. But even if its reality be no
longer matter of doubt, conjectures as to its amount are still vague and
uncertain; and great, indeed, must be the extent of the movement before
this cause alone can work any material alteration in the ter