2 Heavy Fall of Rain 



supplementary to those contained in my former paper, having 

 a special reference to the drainage of Hohart Town. 



It appears by the table submitted, which shows in th* 

 first page the rate at which the rain fell from 9 a.m. on the 

 Sunday, to 8*50 p.m. on Monday, a period of thirty-four 

 hours, that the total amount of the discharge was 8'68 

 inches. 



On comparing this with the returns on the second page 

 of the maximum amounts which have fallen in any day 

 since 1842, when the records were first kept, we find that 

 in November 1842, 4'05 inches fell in eighteen hours ; 

 that in November 1849, 4"0 inches fell in twenty-two 

 hours, while on the present occasion, 6 "25 inches fell in 

 thirteen hours; so that while in November 1842, the average 

 discharge was '225 inches per hour, on Sunday, 26th 

 February, 1854, the discharge was *416 inches per hour, 

 or not much less than double the former quantity. 



It is evident that, in considering the size of the sewer 

 required to discharge a given quantity of water, the abso- 

 lute quantity is not of so much importance as the rate 

 of delivery, and that a sewer which might be quite capable 

 of discharging 8 inches of rain, if spread over forty- eight 

 hours, would be altogether insufficient to pass the same in 

 twenty-four hours. 



If, then, we assume that the rate of '416 of an inch per 

 hour is the maximum amount which is likely to fall in the 

 area, of which the Hobart Town rivulet is the outlet, we 

 have next to approximate to this area, so as to get an ex- 

 pression for the quantity which will have to be passed through 

 any given part of the rivulet during the same period. 



I am not possessed of a survey detailed enough to ena- 

 ole me to give even a guess at the area, neither indeed 

 would it be possible to deduce any very accurate conclusions 



