e in
magneto-electric intensity, the contrast is mainly due. Corn and cotton
will be grown, to some extent, in the valleys west of the meridian of
105 deg., but never as successfully as east of it.

The aurora is periodical, like all the other atmospheric phenomena, but
its periodicity is not accurately ascertained. It is believed to have
occurred much oftener during the second quarter of this century, than
during the first. It is known, however, to occur most frequently in the
spring and fall; and during those periods when the active and rapid
transit of the atmospheric machinery produces the greatest degree of
magnetic disturbance. This identifies it with terrestrial magnetism.
Dalton gives us the following table of observations, arranged according to
the months when they were seen.

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.

(1) 18 18 26 32 21 5 2 21 23 36 38 9
(2) 21 18 23 13 3 2 1 3 35 22 22 21
(3) 21 27 22 12 1 5 7 9 34 50 26 15
(4) 5 6 4 8 10 7 6 14 14 17 5 6

(1) contains those observed by him at Kendall; (2) are taken from another
list; (3) is MARIAN'S list of those observed before 1732; and (4), those
seen in the State of New York in 1828 and 1830.

Mr. Stevenson's table of those observed by him at Dunse, from 1838 to
1847, inclusive, is as follows:

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.
32 20 18 18 3 0 2 14 43 34 30 23

Observations in this country correspond substantially with the foregoing.
They are, however, seen here in the summer months more frequently than in
Europe. See an article by Mr. Herrick (American Journal of Science, vol.
33. p. 297). In this, also, they conform to our greater magnetic intensity
and more excessive climate.

The auroras appear to follow the polar belts of condensation and
precipitation. Dalton considers them indications of fair weather. They are
often most brilliant just after a storm has passed, but their continuance
is no indication that another will not follow within the usual period.

The condensation with which the aurora is connected, is not, in my
judgment, often in the counter-trade, or below it, but above, where feeble
condensation has been seen by aeronauts when invisible at the surface of
the earth. Neither the height of this condensation, not tha