394 THE FARMER AT HOME. 



of the hydrometer ; and having placed a thermometer in it, he brought 

 it, by means of a pan of coals, to the same degree of heat with that 

 of the air in the hottest summer. He then placed his vessel, with the 

 thermometer in it, in one scale, and nicely counterpoised it with 

 weights in the other ; after two hours, he found that about the sixtieth 

 part of an inch was gone off in vapor, and, consequently, in twelve 

 hours, the length of a natural day, one tenth of an inch would have 

 been evaporated. From this experiment it follows, that every ten 

 square inches of the surface of the water yield a cubic inch of water 

 in vapor per day, every square mile 6,914 tons, and every square de- 

 gree, or sixty-nine miles, thirty-three millions of tons. Now, if we 

 suppose the Mediterranean to be fort) degrees long, and four broad at 

 a medium, which is the least that cai be supposed, its surface will be 

 one hundred and sixty square degrees, from whence there will evapo- 

 rate five thousand two hundred and eighty millions of tons per day, 

 in the summer time. The Mediterranean receives water from the 

 nine great rivers following, viz : the Iberus, the Rhine, the Tiber, the 

 Po, the Danube, the Neister, the Borysthenes, the Tanais, and the 

 Nile, all the rest being small, and their waters inconsiderable. 



Now let us suppose that each of these rivers conveys ten times as 

 much water to the sea as the Thames ; which, as is observed, yields 

 daily 76,032,000 cubic feet, which is equal to two hundred and three 

 millions of tons ; and therefore, all the nine rivers will produce 

 eighteen hundred and twenty-seven millions of tons ; which is little 

 more than one-third of the quantity evaporated each day from the 

 sea. The prodigious quantity of water remaining, the doctor allows to 

 rains, which fall again into the seas, and for the uses of vegetation. As 

 to the manner in which these waters are collected, so as to form reser- 

 voirs for the different kinds of springs, it seems to be this the tops of 

 mountains, in general, abound with cavities, and subterraneous caverns, 

 formed by nature to serve as reservoirs ; and their pointed summits, 

 which seem to pierce the clouds, stop those vapors which fluctuate in 

 the atmosphere, and being constipated thereby, they precipitate in 

 water, and by their gravity, easily penetrate through beds of sand 

 and lighter earth, till they are stopped in their descent by more dense 

 strata, as beds of clay or stone, where they form a basin or cavern, 

 and work a passage horizontally, and issue out at the side of the 

 mountain. Many of these springs running down by the valleys, be- 

 tween the ridges of hills, arid uniting their streams, form rivulets or 

 brooks ; and many of these, again, uniting on the plain, become a 

 river. 



STARCH. If a quantity of wheat flour is formed into a paste, 

 and then held under a very small stream of water, kneading con- 

 tinually till the water runs off from it colorless, the flour, by this pro- 

 cess, is divided into two distinct constituents. A tough substance, of 

 a dirty white color, called gluten, renains in the hand ; the water is 



