SIPHON 



5394 



SIRENS 



Phillips' (21 acres) and McKennan (19 acres) 

 parks and the rapids of the river are among 

 the interesting features of the city. 



Sioux Falls is surrounded by a rich farming 

 and stock-raising country, of which it is the 

 commercial center. In the vicinity are large 

 quarries of jasper or granite, used locally and 

 shipped for building purposes. Water power 

 furnished by the river, which drops at this point 

 nearly 100 feet in a half mile, is utilized by 

 manufactories. The leading industrial estab- 

 lishments are meat-packing plants, a biscuit 

 factory, quarries and flour mills. 



The first permanent settlement was built 

 about 1857. The place was incorporated as a 

 village in 1877 and became a city in 1883. It 

 adopted the commission form of government in 

 1909, and owns the water system. L.M.G. 



SIPHON, si'jahn, a bent tube with two un- 

 equal arms, used to carry a liquid from a 

 higher to a lower level. In the accompanying 

 figure the liquid (ra) is forced through the tube 

 (t) by the pressure of the air on the surface (a), 

 which amounts 

 practically to fif- 

 teen pounds to 

 the square inch. 

 As long as the 

 pressure at a is 

 greater than the 

 weight of the 

 column of water 

 (a 6), or until the 

 surfaces (da) are 

 the same level, or 

 a b equals c d, 

 the flow -will con- 

 tinue. Theoreti- 

 cally, a liquid will 

 not flow through PRINCIPLE OF THE 

 a siphon when the SIPHON 



highest point in The tube (t) is the siphon ; 



explanation of the physical 



the tube is thirty- law involved appears in the 



three feet above text 



the level of surface a, because the pressure of a 

 column thirty-three feet high is equal to the 

 pressure of the atmosphere. In practice, how- 

 ever, the highest point cannot exceed thirty 

 feet, and a much better flow is secured if it is 

 not more than twenty-six feet. 



The principle of the siphon is employed on 

 a large scale in aqueducts for carrying water 

 over hills, but in such cases the flow is in- 

 creased by the use of pumps. The so-called 

 siphon bottles used in mixing drinks are oper- 

 ated by compressed air or gas. 



SI 'REN, an instrument designed originally 

 to measure the number of vibrations in a mu- 

 sical tone of a given pitch. The original form of 

 siren consists of a circular disk perforated with 

 one or more circular rows of oblique holes, and 

 so mounted that it revolves close to another 

 disk perforated with corresponding holes slop- 



TWO OF THE SIRENS 

 The figures a and & are referred to in the text. 



ing in the opposite direction. The stationary 

 disk is connected with a bellows or some other 

 device by which compressed air, gas or steam 

 is forced through its holes. When the holes in 

 the revolving disk are opposite those in the 

 stationary disk a puff of air escapes. 



As the velocity of rotation increases, the 

 puffs become more frequent until a clear, con- 

 tinuous sound is produced. The more rapid the 

 vibration the higher the pitch. For instance, 

 if there were thirty perforations in the disk, 

 and it revolved fifteen times per second, there 

 would be 15 x 30 or 450 puffs or vibrations per 

 second. Thirty revolutions per second would 

 give 900 vibrations, and so on. The revolving 

 disk is connected with a system of clock work 

 which registers the number of vibrations per 

 second, and by use of a siren of this pattern 

 the number required for any pitch can be easily 

 determined (see a in the figure). A more re- 

 cent pattern makes use of two perforated cyl- 

 inders, one within the other, in place of the 

 disks. The outer cylinder revolves. 



Very large sirens are used for fog signals at 

 lighthouse stations. Steam is employed in place 

 of air, and a large trumpet-shaped horn (b in 

 figure) is used to direct the sound. Some of 

 these fog horns, as they are called, can be 

 heard twenty-five or thirty miles. They pro- 

 duce low tones that carry a long distance. 



SIRENS, si'renz, THE, in Greek mythology, 

 two maidens who lived on an island and by 

 their exquisite singing enticed mariners to their 

 shore, where they remained, forgetful of home, 

 of friends and of duty until they died of starva- 

 tion. Ulysses was warned by Circe of the danger 



