610 LONGEST BRIDGE IN THE WORLD. 



ponds, highly impregnated with alkali, the water having a milky appear- 

 ance, with a disagreeable taste and smell. I have presented to Professor 

 Thomas Condon, of the State University, to whom I was largely indebted 

 for valuable suggestions as to the manner of selecting and packing speci- 

 mens, the most of my find, retaining but few duplicates myself. 



MECHANICS AND ENGINEERING. 



LONGEST BRIDGE IN THE WORLD. 



The longest railroad bridge in the world was opened for public travel 

 near Dundee, Scotland, on Tuesday, September 25. The structure thus 

 opened spans the estuary of the Tay at a point almost two miles in width. 

 It has been constructed for the purpose of affording facilities for the more 

 convenient conduct of the traffic of the North British Kailway Company. 

 Hitherto the North British Railway Company have had to carry their traf- 

 fic across the Tay by means of a ferry, and this method was not only ex- 

 pensive, but exceedingly slow. Accordingly, their engineer, Mr. Bouch, 

 prepared the plans of the bridge which has now been completed. Parlia- 

 mentary sanction was obtained in 1870, the bridge being constructed as a 

 separate undertaking, with a capital of $1,750,000. 



The contract for the work was obtained in May, 1871, and the founda- 

 tion stone was laid in the land abutment on the south side on the 22d of 

 July of the same year. The bridge begins about a mile and a half above 

 Newport, on the south side of the river, where the depth of water at high 

 spring tides is 45 feet, the velocity of the current reaching occasionally five 

 knots an hour. To bridge this formidable stretch of water, the engineer 

 planned a bridge of 85 spans, varying in length from 67 feet to 245 feet— 

 those of the largest size, to the number of 13, being placed over the navi- 

 gable part of the river. In this central section, where it was necessary to 

 provide for the passage of such shipping as frequents the ports of Newburg 

 jind Perth, the bridge has a clear height of 88 feet above high water, from 

 which it slopes down to the Fife side with a gradient of 1 in 356, and to- 

 ward the Dundee side, where it takes a curve to the eastward, in order the 

 more conveniently to join the land line, with a gradient of 1 in 73. Cylin- 

 ders of ii-on and brickwork, with a diameter of 9^ feet, built on shore in 

 such lengths as would reach from the rock on which they were intended to 

 rent to a point above low water level, each consisting of a cast-iron shell 

 with a lining of brickwork set in Portland cement, leaving inside a central 

 shaft three and a half feet in diameter, through which the workmen might 

 pass up and down, were connected by means of a wall of brickwork about 



