384 Transactions of the Royal Society of South Africa. 
number of rainy days reported, from whatever station in the section, 
each year. For Section IX the number of rainy days at Kenilworth is used ; 
for XV those of Durban ; XIX to XXIII takes Pretoria and Johannesburg ; 
XXIV is for Bulawayo ; XXV is for Melsetter ; and XXVII is for Zomba. 
Altogether the section with the greater rainfall has the greater number of 
rainy days, 
A "rainy day" is a day upon which the precipitation is at least 
'01 in. 
The hour at which the rainy day is supposed to end has a curious influ- 
ence on the number of rainy days in a year. Thus at Kenilworth it makes 
all the difference whether the day is reckoned from 8 a.m. to 8 a.m., or from 
8 p.m. to 8 p.m. In the former case the average number of rainy days for 
the 14 years 1901 to 1914 is 70, whereas in the latter case the average 
number is 75. The reason for the difference is that it rains more often (see 
Table A) at 8 p.m. than it does at 8 a.m. Suppose it to be raining from 7 to 
9 p.m. on June 10, and the hourly fall to be 
7- 8 p.m. . . 15 in. 
8- 9 p.m. . . '12 in. 
This would give us one day's rain of '27 in. for the 24 hours ending 8 a.m. 
June 11, but one day's rain of "15 in. for the 24 hours ending 8 p.m. June 
10, and another of '12 in. for the following 24 hours. 
In addition to 75 days (8 p.m. to 8 p.m.) of rainfall in measurable 
quantities at Kenilworth in a year, there are 25 more days upon each of 
which only a few drops are noted. 
The " Greatest rainfall in one year " (Table B) applies to any station in 
a given section. Mostly the wettest years occur at places where the mean 
rainfall is the greatest. 
The last column of Table B gives some typical heavy rainfalls in 24 
hours. The quantity shown for Section IV is remarkable. Previous to 1906 
the average i-ainfall for December at Swellendam was 2-36, derived from 25 
years of observation. In December, 1906, there were torrents of rain 
(" cloudbursts " in the vernacular) experienced over nearly the whole of 
Section IV, and probably the most intense ever known there. In that month 
26' 72 in. fell at Swellendam and 16-82 in. at Heidelberg, of which 65'01 in. 
fell in one day at the former place and 11*37 in. at the latter. 
5. A Note on South African Hailstorms. 
A good deal of the South African rainfall occurs in hailstorms. 
Lenard has found that raindrops exceeding O'l in. radius cannot last, but 
break up into smaller fragments in a very few seconds, while tiny drops 
can hold themselves intact in strong tumultuous gusts of wind. Hailstones, 
however, can go on growing even to the size of cricket balls. Some of the 
