MECHANICS AND USEFUL ARTS. 75 



A line of levels was successfully carried from the sea over the 

 dividing range, at an altitude of 1200 feet, and down to the Su- 

 cubti, at a point about 3 miles below its sources, where an alti- 

 tude of 560 feet was obtained. A series of careful observations 

 were made with both the aneroid and mercurial barometers, at 

 the different bench-marks, whose height was already determined 

 by the spirit-level. They resulted in showing that the aneroid 

 barometer was totally unreliable, being often 100 feet in error, 

 while the extreme deviation of the mercurial barometer was never 

 more than 30 feet, and the average not more than 12 feet from 

 the correct height. The height of the Sucubti, by spirit-level 560 

 feet, was evidence sufficient that no pass below that altitude ex- 

 isted in the divide. This river with its tributaries, the Napsati 

 and Asnati, drain a large area of country, of which its bed must 

 necessarily represent the lowest level. ' Careful observations with 

 the mercurial barometer were made down the Sucubti to its junc- 

 tion with the Chucunagua, at which was found an altitude of 159 

 feet. 10 miles down the Chucuuagua an altitude of 99 feet was 

 obtained. 



In all observations with the barometer a standard was also 

 noted at the sea-shore. 



All idea of a pass in the divide being exploded, there remained 

 the sole test of a tunnel to decide upon the impracticability of 

 this route. Allowing the largest error ever obtained in our exper- 

 iments in the barometrical heights of the Sucubti, taking 30 feet 

 as the depth of our canal, and conceding that at 200 feet tunnel- 

 ling is more economical than open cutting, there will be found a 

 distance of 10 miles from an altitude of 200 feet on the Atlantic 

 slope to a corresponding one on the Pacific, or, in other words, a 

 tunnel of this length would be necessary. The country in the 

 vicinity of the Sassordi River presenting favorable indications from 

 the sea, a similar exploration and survey was carried on from. 

 Sassordi harbor, some 10 miles north of the previous surveys. 

 This was continued up the Sassordi River across the divide to the 

 Morti, but a like result was obtained, requiring a tunnel of 8 

 miles in length to span the mountain area. 



The northern portion of the Isthmus, from the Gulf of San Bias 

 to the Pacific, forms the narrowest portion of the continent, but 

 30 miles in width. The shortness of this line, the appearance of 

 the interior from the sea, and the magnificent harbor, pointed it 

 out as the proper field for still further explorations. Work was 

 accordingly begun about the 1st of May, and though the rainy 

 season had begun, the favorable indications of this line filled all 

 with enthusiasm to push ahead in spite of the hardships and ob- 

 stacles arising from an inclement season. The line of levels was 

 carried up the Mandinga, the largest river emptying into the 

 Atlantic between the Chagres and the Atrato, and crossed the 

 divide at an altitude of 1100 feet. 



It was continued in a S.S.E. direction down the Pacific slope, 

 till, at a distance run by level of 23 miles from the sea, it met, at 

 the junction of the Mnrmoniand San Jose Rivers, with the survey 

 of Mr. Keiley's in 1864, whose engineers ran a line of levels from 



