have an atmosphere_."
[444] Bonnycastle, whilom professor of mathematics in the Royal
Military Academy, Woolwich, writes: "Astronomers were formerly
of opinion that the moon had no atmosphere, on account of her
never being obscured by clouds or vapours; and because the fixed
stars, at the time of an occultation, disappear behind her
instantaneously, without any gradual diminution of their light. But if
we consider the effects of her days and nights, which are near thirty
times as long as with us, it may be readily conceived that the
phenomena of vapours and meteors must be very different. And
besides, the vaporous or obscure part of our atmosphere is only
about the one thousand nine hundred and eightieth part of the earth's
diameter, as is evident from observing the clouds, which are seldom
above three or four miles high; and therefore, as the moon's
apparent diameter is only about thirty-one minutes and a half, or one
thousand eight hundred and ninety seconds, the obscure part of her
atmosphere, supposing it to resemble our own, when viewed from
the earth, must subtend an angle of less than one second; which is so
small a space, that observations must be extremely accurate to
determine whether the supposed obscuration takes place or not."
[445] Dr. Brinkley, at one time the Astronomer-Royal of Ireland,
writes: "Many astronomers formerly denied the existence of an
atmosphere at the moon; principally from observing no variation of
appearance on the surface, like what would take place, did clouds
exist as with us; and also, from observing no change in the light of
the fixed stars on the approach of the dark edge of the moon. The
circumstance of there being no clouds, proves either that there is no
atmosphere similar to that of our earth, or that there are no waters on
its surface to be converted into vapour; and that of the lustre of the
stars not being changed, proves that there can be no dense
atmosphere. But astronomers now seem agreed that an atmosphere
does surround the moon, although of small density when compared
with that of our earth. M. Schroeter has observed a small twilight in
the moon, such as would arise from an atmosphere capable of
reflecting the rays at the height of about one mile." [446] Dr.
Brinkley is inaccurate in saying that astronomers are agreed as to
the lunar atmosphere. Like students in every other department of
inquiry, spiritual as well as physical, they fail at present to see "eye
to eye";