ENGINEERING. 



313 



1774 by Don Augustin Cramer, in 1824 by 

 Don Tudeo Ortiz and Don Juan de Orbegoso, 

 in 1842 and 1843 by Settor Moro, and in 1832 

 by J. J. Williams on the part of the Tehuan- 

 tepec Railway of New Orleans. James B. Eads 

 be'came interested in the subject, and has de- 

 signed a ship-railway, the plans of which, now 

 that their features are better understood, are 

 generally admitted to be quite practicable. Mr. 

 Eads has obtained a very favorable concession. 

 He proposes to raise vessels out of the sea, place 

 them on carriages, transport them over a ship- 

 railroad across the isthmus, and place them in 

 the water at the end of the journey. The ships 

 will enter Coatzacoalcos river, which flows into 

 the Gulf of Mexico, and ascend twenty -five 

 miles from its mouth to the town of Mina- 

 titlan, the Coatzacoalcos river being a broad 

 stream, which will require improvement at 

 only one point. At its mouth there is a bar, 

 which will be scoured in the same way by jet- 

 ties as those at the mouth of the Mississippi. 

 At Minatitlan the railroad begins ascending 

 the Atlantic plains for thirty-five miles by an 

 easy grade of forty-two feet to the mile. It 

 then enters a gently undulating table-land, 

 from which it passes by a series of broad val- 

 leys to the summit level, the Tarifa plains, 726 

 feet above the sea. The descent from this 

 point to the Pacific plains has a uniform grade 

 of one in a hundred, and requires three deflect- 

 ing turn-tables. From the base of the hills to 

 the Pacific end the line extends over a nearly 

 level country. The station is to be either at 

 Salina Cruz or at one of the lagoons. 



The details of the plans for transferring the 

 vessels from the water to the railroad have been 

 worked out with a great deal of ingenuity. The 

 general principles underlying are the follow- 

 ing, stripped of technical detail : The vessel 

 is run into a narrow dock, one of the ends of 

 which is open to the stream, while the other 

 faces the end of the railroad-track. Under 

 the vessel, when in position, is a submerged 

 pontoon, which can be raised or lowered by 

 pumping water out of or into it. On the pon- 

 toon, which has tracks of the same gauge as 

 that of the railroad-track, is a carriage. When 

 the vessel is in position, the water is pumped 

 out of the pontoon until the carriage approach- 

 es the keel of the ship, when, by an automatic 

 arrangement, the vessel is so seated on keel- 

 blocks that its weight is uniformly distributed 

 over the whole length and breadth of the car- 

 riage. Pumping is then resumed, until the 

 rails on the pontoon stand flush with those of 

 the railroad, when the carriage, with the ship 

 on it, can be drawn on the shore and started 

 on its trip across the isthmus, to be lowered 

 into the water at the other end by means of a 

 second pontoon. 



The Shorina; of Chestnut-Street Bridge over the 

 Schuylkill. One of the most interesting and 

 novel pieces of work partially carried out dur- 

 ing 1884 was the shoring of Chestnut Street 

 bridge, over the Schuylkill, in Philadelphia. 



The bridge was completed in 1805, has two 

 185-foot arch-spans, and with its approaches 

 is 1,528^ feet long. The foundations of the 

 western abutment were white-oak piles, driven 

 through twenty-seven feet of silt down to a 

 five foot layer of gravel and bowlders, covering 

 the bed-rock. The heads of the piles were im- 

 bedded in ~beton to a depth of 2^ feet, upon 

 which was laid a platform on which the ma- 

 sonry was erected. The thrust of the long, 

 fiat arch forced the whole western abutment 

 through the yielding material on which it rest- 

 ed, and though temporary relief was sought by 

 placing wooden struts at water-line from the 

 abutment to the arch pier, and from the pier 

 to the base of the approach, it was decided to 

 seek other means of saving the bridge from 

 destruction. The abutment had moved eight 

 inches, and the central pier four inches, and 

 the problem was to arrest any further move- 

 ment without disturbing the traffic of the rail- 

 road that was running under one of the ap- 

 proach arches, or endangering the stability of 

 the abutment. The ingenious plans of Messrs. 

 Anderson and Barr were adopted, which con- 

 sisted in building four iron 8-foot cylinders, 

 resting upon the bed-rock, and extending up- 

 ward at an angle of 45 through the silt to the 

 abutment, into the base of which they were 

 stepped. These cylinders were to be filled 

 with cement as soon as sunk, in order to ren- 

 der them solid supports of the abutment, and 

 take up the thrust of the arch. The length 

 of two of the four underground struts com- 

 pleted in 1884 was 65 and 62 feet. The cylin- 

 ders are sunk with the aid of compressed air, 

 by digging out a space large enough to admit 

 of placing one plate, which is then bolted on 

 to those already in position. Thus, plate by 

 plate, and ring by ring, is got into place, until 

 the cylinder reaches bed-rock, when the work 

 of laying the concrete begins. The concrete 

 used is a mixture of one part of cement, two 

 parts of sand, and four parts of broken stone. 

 Communication between the interior of the cyl- 

 inder and the outer air is effected by meano of 

 an air-lock fourteen feet long and five feet wide, 

 divided into three compartments. The electric 

 light is used for the work in the cylinder. 



The Nicaragua Canal. The discussion of the 

 treaty proposed between the United States and 

 Nicaragua has directed attention to the pro- 

 jected canal, which has always been a favor- 

 ite one with our government engineers, who 

 during the past thirty years have made elabo- 

 rate and conflicting reports in reference to it. 

 While the treaty has been defeated, the Gov- 

 ernment has sent another expedition to Nicara- 

 gua, under the direction of A. G. Menocal, of 

 the navy, to make a resurvey of the location, 

 on which the estimates of former surveys 

 may be revised and verified. The cost has 

 been variously estimated at $75,000,000 and 

 $140,000,000, the latter figure being that of 

 Major Walter McFarland, in his reports to^the 

 United States Interoceanic Canal Commission, 



