240 Observations on the Earthy Matter [June, 



reins. The river had reached this maximum on the 13th August, 

 and continued at the same until the 20th. After that it subsided as 

 follows : 



ft. in. 



On the 26th August the fall was 7 6 



7th Sept 5 2 



21st Sept 5 6 



27th Sept 13 



4th Oct 15 4 



25th Oct 22 10 



So that we may call the average depth for the third month of the 



rains 4 feet 3 inches below maximum, or in round numbers 41 feet. For 



the fourth month, viz. from the 15th Sept. to 15th Oct. the average 



depth would be 1 1 feet 3 inches below maximum, or 34 feet. For the first 



two months of the rains, the rise of the river was not measured, but from 



the quantity of rain that fell and the apparent increase, I cannot believe 



that the average depth would be less than the average for the fourth 



month, viz. 34 feet. If then we assume this number for the first two 



months, we have an average depth of 36 feet for the four months of 



the rains. A mean between 22 feet 10 inches (the fall measured on 



the 25th Oct.), and 28 feet (the fall measured on the 15th March), 



gives 24 feet 1 1 inches for the fall below the maximum in the interv ning 



period, or in round numbers 20 feet for the actual depth during that 



period. For the three months of dry weather ensuing, 17 feet 8 



inches may be taken as the depth. — We have seen that the least 



breadth in the dry weather was 1980 feet, and the greatest in the 



rains 2563 feet ; leaving a difference of 583 feet. So that while the 



depth diminished 28 feet, the breadth diminished 583 feet, or 21 feet 



of breadth nearly for one of level. This proportion gives us 2383 feet 



for the average breadth during the four rainy months. Owing to the 



diminished velocity near the bank, and the diminished quantity of 



matter held in suspension there, this excess must be again reduced. 



Probably 2080 feet may be reckoned as the fair average breadth for 



the rainy months, 1780 for the winter, and 1730 for the hot months. 



The velocity, by the mean of two measurements on the 2nd and ] 4th 



April, 1832, at the surface, was 4425 feet per hour. I have no similar 



measurement for the maximum velocity in the rains, but while the 



river was at its greatest height I came a computed distance of 10 



miles in an hour and a half, and from other observations of the same 



kind, both by myself and others, I am induced to estimate the maximum 



velocity at 6^ miles, or 34320 feet per hour. Assuming that the 



