744 



sometimes the river again sinks f in April; it 

 attains it's maximum in July ; remains full (at 

 the same level) from the end of July till the 

 25th of August; and then decreases progres- 

 sively, but more slowly than it increased. It is 

 at it's minimum in January and February. In 

 both worlds the rivers of the northern torrid 

 zone attain the greatest height nearly at the 

 same period. The Ganges, the Niger, and the 

 Gambia, reach the maximum, like the Oroonoko, 

 in the month of August *. The Nile is two 

 months later ; either on account of some local 

 circumstances in the climate of Abyssinia, or of 

 the length of it's course, from the country of 

 Berber, or 175 p of latitude -f-, to the bifurcation 



* Nearly forty or fifty days after the summer solstice. 



t The point (17° 35 ') where the Tacazze, or Astaboras, 

 enters the Nile. (See the excellent work of Mr. Burckhardt, 

 p. 163.) The Nile receives no river below this, either on the 

 east or on the west j a solitary instance in the hydrographic 

 history of the globe. The distance from the mouth of the 

 Tacazze to the Delta is nearly 1350 nautical miles; so that 

 admitting the mean velocity of the Nile (Girard, p. 13) to be 

 four feet in a second," or two miles and a half in an hour, I find 

 twenty-two days and a half for the time of the descent of a 

 particle of water. This is also nearly the time a swell would, 

 take to descend from the sources of the Oroonoko to it's 

 mouth, through an itinerary length of 1308 nautical miles. 

 The velocity of the Nile in Nubia is no doubt a little greater, 

 than I have estimated it in this calculation. The retardation, 

 of the oscillations of the Nile is very remarkable, compared 



