(or Rain-band Spectroscope) in Meteorology. 127
blowing or likely to change to. Since this matter was
suggested it has been adopted by observers and found to work
very satisfactorily, especially if the results are charted, in
order that the increasing or decreasing percentages, &c, may
be studied, and calculations made accordingly ; 3rd, that
some attention ought to be paid to the varying tints and
depth of colour in the prismatic spectrum, the differences at
times being very remarkable; 4th, that, as a rule, several
days before snow, the rain-band diminished considerably, the
spectrum became clearer, and the calcium and barium lines
on the blue side of D were unusually prominent.
Amongst hygro-spectroscopists at one time it was thought
that the observer with the help of the rain-band ought to be
able to prognosticate almost every form of precipitation ; this
was too much to be expected of one feature in the spectrum.
The principal rain-band on the red side of D does not indicate
the deposition of dew, neither the fall of solid bodies such as
hail or even snow, which last, as I have just remarked, must
only be expected from negative results as regards the rain-
band. Thunderstorms are almost invariably accompanied by
hail; and Mr. Bramley Moore, of Liverpool, has pointed out
in 'Knowledge' that the most noticeable phenomenon in the
sky spectrum, before their occurrence, is the extreme depth
in colour of the blue, and an unusual prominence of the
green, which he describes as apparently overlapping the blue.
I cannot say that my experience of the unquestionable
difference in colour is such as to justify my describing it as
the one "overlapping" the other. To these I would add,
the dark band at V, which is generally most marked before
heavy rain, and more or less percentage of the principal
rain-band, according to the amount of rain accompanying the
storm. I well recollect one instance in which all these
features were so extremely well marked at the time of
observation,. about 10 a.m., that I confidently prophesied a
storm would take place, although none of the other instru-
ments, nor any particular aspect of the sky, nor high
temperature with oppressiveness, indicated that such an
aerial disturbance was about to occur, yet, certain enough, in