53 
of Edinhurgh, Session 1882 - 83 , 
perhaps more clearly seen when one or two very slight showers on 
an otherwise fine day are classed as “no rain,” and this is evidently 
a fairer way of estimating the predictive power than by considering 
a day on which “ no rain ” was predicted and a trifling shower 
occurred as a failure. A better plan would be to omit all days on 
which there were only slight showers, and simply take account of 
those on which there was no rain at all or else heavy rain, suffi- 
ciently heavy, for example, to interfere with outdoor work. In Table 
III. it is seen that the increase in intensity of the rainband is not 
followed by a perfectly regular increase in the percentage of rainy 
days, which is probably due to the scale not being perfectly uniform, 
and that a dark rainband is a much surer prognostic of a wet day 
than a faint one is of dry weather. 
Table III. 
Intensity 
D + tt 
Percentage of 
rain following. 
Percentage of “no 
rain” following. 
= or< 5 
27 
73 
>^<F 
■ S8 
62 
= F 
74 
26 
>F 
92 
8 
This table represents the results for seven months, classing one, or 
at most two, slight showers as “no rain.” Since the extreme values 
of the intensity of the rainband illustrate its predictive power most 
strikingly, it may help to show the importance of such observations, 
if a short account is given of the various cases in which D -H tt was 
registered as >F and as <5 during the seven months under con- 
sideration. During these months there were thirty-seven cases of 
D-f-7T>F, and on three of these no rain followed vdthin twelve 
hours. Two of these mornings of failure were very misty, but the 
third was bright and clear. On ten occasions heavy showers came 
on in the afternoon. On one of these occasions (July 1st) there 
was a thunderstorm, on another (September 1st) the rainband, 
according to Professor Piazzi Smyth, was the darkest for the whole 
year. There were heavy showers in the forenoon on three days 
and showers at irregular intervals on -ten, two of which (July 6th 
