ENGINEERING. 



315 



and tli us obtain the additional supply of many 

 springs tapped by the tunnel, small square 

 openings are provided at intervals in the mason- 

 ry linings. These openings are called " weep- 

 ers." All springs tapped, which are not under 

 sufficient pressure to add to the volume of 

 water flowing through it, are collected in a 

 drain carried along under the masonry to 

 points along the tunnel where the water can 

 be got rid of, since it would otherwise wash 

 away the backing of the masonry. These points 

 are called "blow-offs," or ; ' waste-weirs," and 

 serve also the important function of permit- 

 ting the emptying of a section for repairs, etc., 

 without discharging the water from the entire 

 length of the aqueduct. The points selected 

 for these waste-weirs depend, of course, on 

 the topography. At the selected point, the 

 aqueduct merges into a rectangular chamber of 

 two stories, the upper being entirely above the 

 crown of the tunnel arch. The width of this 

 chamber about corresponds to the maximum 

 diameter of the tunnel. Alongside of this two- 

 story chamber is a second one of similar de- 

 scription, which communicates with the first 

 by four gates reaching from the top to the 

 bottom of the chamber, and each of which is 

 independent of the others. A breast- wall, in 

 the second chamber, over which the escaping 

 water flows when any of the four gates are 

 opened, can be raised at will by the use of 

 planks sliding in grooves, so that the level of 

 the overflow may be varied, or the water may 

 be entirely discharged by opening gates in the 

 breast- wall. In the first chamber is built a 

 pier of masonry, to serve as an abutment for 

 massive gates,, which may be lowered, and by 

 closing similar gates at the farther end of the 

 tunnel structure, the portion of the aqueduct 

 between them may be emptied without draw- 

 ing any water from any of the other sections 

 along its length. In order to reach the tunnel 

 level for purposes of excavation and working 

 during construction, there is provision for 

 thirty-three shafts. Some of these, when the 

 tunnel is completed, will be under pressure of 

 a head of water for a part or the whole of their 

 depth; in others the water will rise only a 

 little, if at all, above the crown of the tunnel 

 arch. The former are lined with a greater 

 thickness of masonry and at convenient points 

 brick arches are thrown across the shaft, and 

 heavy-ribbed iron plates are provided to pre- 

 vent the escape of water. At several points in 

 the shaft it is widened to give standing-room 

 for the men when examining and cleaning. In 

 order to allow of the escape of air imprisoned 

 under pressure when the aqueduct is filled 

 after having been emptied, there is an air-pipe 

 leading up through the shaft, fitted with a 

 valve. There are also drain- valves to allow 

 the water in the shaft to escape into the aque- 

 duct when the latter is being emptied, thus 

 enabling access to be had to it through the 

 shaft. Those shafts that are not under water- 

 pressure, in which the water would not rise 



above the crown of the aqueduct tunnel, are 

 simply carefully lined with masonry braced by 

 arches, and are allowed to remain open. They 

 too are provided with weepers to let in the 

 water of any springs that may be tapped. 



Panama Canal. The management of the Pana- 

 ma Canal enterprise continues to be the object 

 of very sharp criticisms, often bearing on their 

 face the bias of the objectors. These strict- 

 ures are met with uniformly roseate accounts 

 of progress, on the part of the projectors of 

 the canal, which, from their character, do not 

 inspire unlimited confidence. It is a difficult 

 matter, with such wilde differences not only in 

 opinions, but in statements of fact, to repre- 

 sent accurately the present status of the en- 

 terprise, or to forecast its near future. M. de 

 Lesseps, at the meeting of the company on the 

 23d of July, 1884, assured the stockholders em- 

 phatically, and he has since reasserted it, that 

 the canal will be opened to navigation before 

 the close of -the year 1888. He said then 

 that careful study had revealed the fact that 

 the amount of work to be done is smaller than 

 was estimated, the natural basin of the Chagres 

 river in its upper part being much greater 

 than was at first believed. On the other hand, 

 American engineers that have visited the works 

 have reported, with singular unanimity, that, 

 at the present rate of progress, the predictions 

 of the projectors can not be fulfilled, and they 

 all agree in pronouncing the estimates of cost 

 far below the sums that will be required. 

 Charles Colne, Secretary of the American .Com- 

 mittee of the Universal Interoceanic Panama 

 Canal Company, in a paper read before the 

 Franklin Institute, Philadelphia, says the ex- 

 cavations necessary to complete the canal will 

 be, for cutting the canal and the ports proper, 

 143,000,000 cubic yards, and for the lateral 

 cuts 13,000,000 cubic yards, a total of 156,- 

 000,000 cubic yards, of which 52,000,000 will 

 be excavated by dredges, and the remainder is 

 dry excavation of earth and rock. Of this 

 work, 10,224,882 cubic yards had been com- 

 pleted up to Sept. 1, 1884. It is urged that, 

 now that a good deal of the expensive and 

 slow preliminary work has been accomplished, 

 the excavation will progress much more rap- 

 idly. The following figures are submitted to 

 show the fallacy of the argument that, because 

 only a fraction of the work has been done 

 thus far, it will take a correspondingly long 

 period, at that rate, to finish it. In the first 

 four years, previous to Jan. 1, 1884, 3,610,778 

 cubic yards had been excavated, while in the 

 first eight months of 1884 the quantity exca- 

 vated had been 6,614,104 cubic yards. 



The African Interior Sea. It does not seem that 

 the death of Col. Roudaire, the originator of 

 the scheme for an inland African sea, will lead 

 to its abandonment. A party of engineers and 

 hydrographers, under the direction of Com- 

 mandant Landes, of the Saint Cyr Military 

 Academy, have gone to Tunisia, with the ob- 

 ject of finishing .the surveys for the creation 



