{or Rain-bancl 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 Y, 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 
