84 FIRST YEAR COURSE IN GENERAL SCIENCE 



90. Mineral Springs and Salt Lakes. Many springs 

 contain dissolved mineral matter in sufficient quantities to 

 be detected by the taste. Some mineral springs are medicinal 

 in character and their water is recommended by physicians 

 in the treatment of some diseases. It does not follow, how- 

 ever, that these waters are beneficial to every one. 



Salt lakes, which contain dissolved salt and other minerals, 

 are found in dry regions where evaporation goes on rapidly. 

 Pure water is continually evaporating from the lakes, while 

 streams are constantly bringing in minerals in solution. 

 When such lakes have no outlet, they become more and 

 more salt. 



91. Gravity, the Cause of Streams. Water, like all 

 other matter, has weight; that is, it is attracted by the earth. 

 Hence, unless restrained, it falls to the lowest possible level. 

 This falling, due to gravity, is the cause of flowing water 

 in streams. The water seems to slide or roll along over 

 the surface of the earth, but in reality streams fall, some a 

 few feet in a mile of their course, others hundreds of feet. 

 Rapids, cascades, and waterfalls are names given to parts 

 of a stream wher.e the fall is considerable within a short 

 distance. 



The headwaters of the Connecticut River are nearly a 

 thousand feet above sea level, so in its journey of four hun- 

 dred miles to the sea the water falls one thousand feet. In 

 a few places the fall is twenty or more feet at one place and 

 there the energy of the falling mass is utilized in turning 

 machinery. 



92. Water Power. Long before steam was used to run 

 machinery, men placed large water wheels where the water 

 could fall upon them, turning them as it fell. Connected 

 with these wheels was the machinery to grind grain, to saw 

 logs, and later to weave cloth. At the present time water 

 is used to run dynamos, which are machines for producing 

 the electric currents that furnish both light and power. 



