THE CORRELATIONS OF AREAS OF MATURED CROP AND THE RALNFALL. 385 



The time of mean rainfall is as before at the 30th July, but the modal or maxi- 

 mum rate of rainfall occurs about a fortnight later on the 13th August, the rate 

 being then n //- o8 per mensem. 



The effective ending of rainfall due to the south-west monsoon is about October 

 8th. The diagram below shows that a much better fit has been obtained. 



3rd. The distribution of rainfall in Zafarwal (November— April). The rainfall 

 in inches is (average of 1887-8 — 1906-7) — 



November, December, January, February, March, April. 



•03 -68 2-69 1-85 1-62 -57 



Multiplying by 1,000 and dividing by the number of days in the month (for 

 February average number of days = 28-2) the following frequencies are obtained 

 approximately — 1, 22, 87, 66, 52, 19. 



The moments about the mean are 



/"i =0 

 m 2 =1-132 

 m 3 = -364 

 ^4 = 3-183. 

 £2=2-19. 



Thus 3 -£ 2 = -8i, which is 3 or 4 times its probable error. 



y= 9I - 4 (i + / o -) 4279 f! -6-o8, 



Fitting the curve y = y Q ( 1 -f- - \ e a x we § et 



The mode is on the 2nd of February, and the mean on the 7th of February, 

 thus the skewness is of opposite sign to that for the months April — October. 



The curve is shown in diagram 19. 



The modal rainfall for the summer rains precedes the modal rainfall for the 

 winter by 173 days, but the points of mean rainfall are 192 days apart. 



The sum of these two periods is 365, though, of course, the result being exactly a 

 tropical year is somewhat fortuitous. 



It is interesting to exhibit the two curves last obtained on the same scale, as they 

 clearly show the distribution of rainfall throughout the year. 



The two curves have their two steeper slopes facing each other. 



Lastly I have taken the actual daily rainfall data for the 20 years 1887-8 — 1906-7, 

 and found the mean rate of rainfall at intervals of 10 days, this rate being the mean 

 of 20 days, so that in the frequency polygon shown in the diagram, the vertices of 

 the polygon represent the mean rainfall for 10 days on either side of the vertex 

 in question. 



