June 9, 1856.] GISBORNE. 89 



leagues apart, with a summit level, to be crossed, not exceeding 300 yards 

 above the sea.* 



Mr. Gisborne remarks, with reference to the practicability of a com- 

 plete survey of the isthmus, before deciding on a line for making an 

 inter-oceanic canal, that " wherever the best spot may be, two elements 

 must necessarily exist — good harbours (or the means of making them) 

 and a short distance. This limits the inquiry to a very few places, and 

 those can be reduced to two or three by a cursory examination. Two 

 surveying vessels on each coast could in a few months examine the un- 

 surveyed portions of Central America sufficiently to decide where good 

 harbours, or facilities for making them, exist. It is not probable that 

 many such places will be found opposite each other ; where such is the 

 case, a general examination of the interior would soon eliminate the 

 impossibles, leaving perhaps two or three places where a more careful 

 and detailed examination may be necessary." 



Dr. Hodgkin begged to introduce to the Society, General Mercer, of the 

 United States, who had been the chairman of a committee for reporting on an 

 inter-oceanic communication through Central America. 



General Mercer said that his friend Dr. Hodgkin had taken him entirely 

 by surprise in mentioning his name ; but being invited also by the Chairman 

 of the Meeting, however incompetent, for many reasons, to cast any addi- 

 tional light on the subject under debate, he would not resist the compli- 

 ment paid him. More than eighteen years had elapsed since the duty had 

 devolved on him, as a member of a standing committee of the House of 

 Eepresentatives of the United States of America, to make a report to that 

 body, on a memorial from certain citizens of New York and Philadelphia, on 

 the practicability and mode of providing for the construction of a navigable 

 ship canal between the Atlantic and Pacific oceans. 



He had despaired of obtaining, through any channel then accessible, the 

 facts necessary to guide even his own opinion upon a subject of the importance 

 of which he had long been aware, when he accidentally found, in a work on 

 Guatemala, by a British official agent, a table furnishing the distance, and a 

 series of levels taken at every hundred yards of the intervening high land 

 between Lake Nicaragua and the Pacific Ocean. From this it appeared that 

 the distance overland, was but 17 miles and 350 yards ; and the elevation of 

 the surface of the lake above the Pacific but 134 feet ; that for 9 miles 

 from the ocean, the ground regularly descended towards it from the level of the 

 lake, over a surface in all respects favourable for a canal of any dimensions. 

 For the 8 miles next to the lake, serious difficulties, although not insurmount- 

 able, were presented, in the elevation of the ground, often rock, above the level 

 of the lake, to heights averaging, for 6 miles, more than 60 feet ; for 2 miles of 

 that distance, 135 feet ; and for one-third of a mile, 150 feet. 



General Mercer said, that the canal was designed by him, to have a depth of 

 26 feet, the draught of a large frigate ; but was enlarged, at the suggestion of 

 the United States engineers, to a depth of 30 feet, with a breadth sufficient to 

 permit two of the largest ships to pass each other. 



The deep cutting from the lake to the Pacific, was not unexampled, even in 

 Mexico. But supposing a tunnel to be dispensed with, and its continued depth 

 extended for several miles more than that example warranted, yet it involved 

 only an additional cost. He did not hesitate, therefore, in inducing the com- 



* See Map to accompany Capt. Prevost's paper, in vol. xxiv. p. 256. — Ed. 



