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ferent hours of the day, from 36° to 52°, and 

 that of sands covered with three or four inches 

 of water 32°. The beds of rivers are heated as 

 far as the depth, to which the solar rays can 

 penetrate without having undergone too great 

 an extinction in their passage through the super- 

 incumbent strata of water. Besides, the effect 

 of nitration extends far beyond the bed of the 

 river ; it may be said to be lateral. The shore, 

 which appears dry to us, imbibes water as far 

 as the level of the surface of the river. We saw 

 water gush out at the distance of fifty toises from 

 the shore, every time that the Indians struck their 

 oars into the ground; now these sands, wet 

 underneath, but dry above, and exposed to the 

 solar rays, act like a sponge. They are losing 

 the infiltrated water every instant by evapora- 

 tion. The vapour, that is emitted, traverses the 

 upper stratum of sand strongly heated, and be- 

 comes sensible to the eye, when the air cools 

 toward the evening. As the beach dries, it draws 

 from the rivers new portions of water; and it 

 may be considered, that this continual alterna- 

 tion of vaporization and lateral imbibition must 

 cause an immense loss, difficult to submit to 

 exact calculation. The increase of these losses 

 would be in proportion to the length of the 

 course of the rivers, if from their source to their 

 mouth they were equally surrounded by a flat 

 shore ; but these shores being formed by depo- 



