1879.] H. F. Blanford—Rainfall Frequency at Calcutta. 43 
From this table, the following conclusions may be drawn. On the 
average of the year, which average is mainly determined by that of the 
summer monsoon months, the hour at which rain is least frequent is short- 
ly before midnight, and that at which it is most so, from 2to3P.m. The 
latter accords approximately with the diurnal epoch of maximum tempera- 
ture [see Plate III, fig. 6], but the former does not accord with its mini- 
mum ; and, indeed, the frequency of rain at the hour of mean minimum 
temperature is nearly 40 per cent. greater than at midnight, while at the 
hour of its maximum it is only twice as great ; and it would rather appear 
that while the greatest heat coincides with a principal maximum of rainfall, 
the greatest cold coincides with a secondary maximum. The course of 
variation as shewn by the table and by fig. 1 of the plate is somewhat as 
follows : 
For about three hours after midnight, the frequency of rainfall in- 
ereases rapidly, but after 3 a. m. more slowly, till about sunrise ; after 
which there is a slight falling off to a secondary minimum at 9 a.m. This 
is very distinctly shown in the present table: in that originally drawn up 
it was less clearly indicated. After 9 a m. the frequency increases rapidly 
to the absolute maximum between 2 and 3 P.M. From this maximum it 
declines, without interruption, to the minimum before midnight. The total 
number of rainy hours from midnight to noon is 46 per cent. of the whole ; 
and between noon and midnight 54 per cent. On the other hand, in the 
day time (6 a. m. to 6 P. .), the proportion is 57 per cent., and 43 per cent. 
in the night hours. 
The character of the variation in the rainy months of the summer 
monsoon does not differ materially from the above. But that of the 
hot season is very different ; and that of the cold season again differs from 
both and is more uniform than either. The following table and figs. 2, 3 
and 4 in the Plate exhibit the data thus arranged according to the three 
seasons. 
Hours A. M. 
gs | 
2 Sie 
i) or) H 19 o]|m!]o|]a = 5 va 
[=| lo} ° 
Ree eon |i) sau Sic leah leas al Se ce 
Rains : Tune to October, | 298) 327] 348} 353) 364) 376| 373] 373] 357] 410) 458) 505 
_ Hot season: March to 
iV] SOAOGnOGOECROnon 28) 29) 32) 28) 21) 24) 28) 25) 24) 30| 29) 33 
Cold season: November 
to February, ........ 17} 18) 29) 29) 29} 26) 29) 28) 28) 21) 34] 27 
