42 ANNUAL OF SCIENTIFIC DISCOVEPwY. 



chief engineer declares that with one of his dredges he can keep 

 the channel clear, and maintain the full depth of water throughout 

 the whole length of the canal. The mud from the Nile, which 

 it was feared would fill up any harbor at the Mediterranean en- 

 trance, has made no deposit at Port Said during the past 6 

 years, this being now one of the best harbors on the Egyptian or 

 Syrian coast, allowing vessels drawing 15 feet to run in, in any 

 weather. 



This canal, when completed, is almost certain to change the 

 direction of the greater part of the shi^Dments between Europe and 

 the East Indies, and must have a marked influence on the trade 

 of the United States with India and China. The company are 

 allowed to charge 10 francs per ton on all vessels passing through 

 the canal ; and, if the amount of tonnage which now doubles the 

 Cape of Good Hope should be diverted into this channel, it will 

 prove a great financial success. — Journal of Franklin Institute^ 

 Aprils May, and June, 1868. 



ILLINOIS AND ST. LOUIS BRIDGE. 



According to the report of Mr. J. B. Eads, Engineer-in-Chief, 

 of which a review is published in the " Journal of the Franklin 

 Institute " for September, 1868, the method adopted in this bridge 

 is the one employed by Sternberg for the great ribbed arch over 

 the Rhine, at Coblentz. 'ihe problem involved in the considera- 

 tion of an arched rib is one of peculiar difficulty, especially when 

 the rib is neither hinged at the crown nor aljutments. Some mod- 

 ifications were necessary in the method of Sternberg, who treated 

 the centre line of the arch as a parabola, and also considered the 

 arch as hinged at the skewbacks. In the St. Louis bridge the 

 ends were considered fixed at the piers, which reduced the com- 

 puted deflections caused by the load under the hinged condition, 

 allowing of a reduction of the weight of the material, provided a 

 short distance from each end was strengthened. This last pro- 

 vision was required from the fact that, with fixed ends, the deflec- 

 tions were greater near the abutments than when the ends were 

 hinged, and also because the efi'ects from change of temperature 

 were increased. 



The ribs are formed from 2 circular flanges, separated about 

 9 feet from each other by a system of triangular bracing. In this 

 not only lies the carrying system, but it also contains the jDrovision 

 for counter-bracing, the spandril filling merely serving to support 

 the roadway. The arch, therefore, acts in the double capacity of 

 a rib under direct compression, and a beam under a transverse 

 load, and the strains at each point are the resultants of the strains 

 arising from the direct compressive action of the load, and from 

 its bending action. The plan adopted consists of 3 cast-steel 

 arches of 500 feet span. 



