Arizona republican., 1902-08-06
SCIENCE AND INDUSTRY.

The address of the chairman of the section of mechanical engineering at the July meeting of the American As sociation for the Advancement of Sci ence gives statistics of American bridge construction. From it the fol- lowing particulars are taken: A dozen years ago few plate girdeI bridges were built whose span exceeded loo feet. The span of the large plate gird- CTS Of the viaduct on the Riverside Drive in New York City is 126 feet. The viaduct that carries the Chicago .& Northwestern Railroad across the val Icy Of the Des Moines river at a height Of lSJ feet above the river. is 2.65S feet long. Most of the spans are 75 feet in length and four lines of plate girders support the two tracks. The viaduct terminal of the Chesapeake and Ohio roalrOad at Richmond, Va, is SIS miles ! long. The highest viaduct is at the crossing Of the Kinzua creek by the Erie railroad. Its height is 3O1 feet and it's length is 2.053 feet. The longest 1 span of any simple truss is that over , the Ohio river at Louisville-namely
 546i5 feet. The Delaware river bridge on the Pennsylvania railroad near Phil i adeiphia has span of 533 feet and contains 2,C94 tons Of steel. The chan mel span Cf the cantilever bridge over 1 the Mississippi river at ;! emphis meas ures 1S313 feet between supports, and is | the longest of it's class in America. The Wabash system is now building such bridge at | ittsburg. whose span is to ke SIP feet. The channel span of the cantilever bridge over the St Law renee river al Quebec is to have the | unprecedented length Of 1,S00 feet This is lJG feet longer than the span of the Firth of Forth cantileVer bridge and 24J feet longer than the .Dan of the l Brooklyn suspension bridge. The tow CTS are to be 300 feet above high tide. It will accommodate a double-tra K railway, two electric railroad tracks and highways. The Brooklyn suspen- sion bridget, ,5951a feet loag-is still | the largest suspension bridge in the
 world. The new East river bridge has a span Of 1.600 feet, and it's capacity is far greater than the Brooklyn bridge
 Each Cf its four cables has a safe
 strength of over 10.0G0, 000 pounds il
 tension. The Washington bridge over the Harlem river consists of two spans
 Of j10 feet in the clear. The ROeblng suspension bridge at Niagara was re-
 placed in 1897 by the spandrel-braced 1 tWO-hinged steel arch of $50 feet span. ii accommodates the railway tracks on the upper deck and d highway below The second Niagara bridge replaced
 the Clifton bridge in 1898, and as its span is Si0 feet it is the largest arch of
 any type in the world. In 1901 the | Pennsylvania railroad built a stone
 bridge consisting of 48 segmental
 arches of 70 feet span over the Susque-
 hanna river. It accommodates four
 tracks and cost about $1 ,0C0. 900; but the
 cost of maintaining it is very small The address of Prof. Jacoby, of Cor
 nell university, from which these fig
 ures are taken, should be referred to by
 all interested-and who is not?-in re-
 cent progress Of the sort. It is printed
 in Science of July 1.
 body. This severing of the electror
 from it's atom is the genera tion of elec-
 tricity- The remainder of the atom
 acts as a positively charged body, but
 it is not certainly known whether the
 positive electron-supposed to be abOu!
 ten times as heavy as the negative
 really exists. Associated with neutra
 particles, the electrons become mega
 tive ions and positive ions. Conductior
 is q wandering of these ions, magnet
 ism and the magnetic field an(