72 KELLEY. [May 12, 1856. 



that a fall of 3 inches in a mile, whicli was that estimated in the present case, 

 was not unusual in artificial canals ; and that the supply of water would be 

 amply sufficient to maintain the canal at a proper elevation. 



Sib Roderick Murchison, f.r.g.s,, begged to observe that the discussion of 

 this question had naturally assumed very much of an engineering character, and 

 acknowledged that the Society was much indebted to the eminent engineers 

 who had already spoken this evening and on a former occasion. He sug- 

 gested, however, that no true inductions could be arrived at, nor any sound 

 attempt made to realize the grand idea of Humboldt, until a general and 

 accurate geodeslcal survey of the whole region alluded to had been completed. 

 In this praiseworthy cause Mr. Kelley had done more than any other person, 

 and he now asks this Society to exercise its influence with the British Govern- 

 ment to assist, with other powers, in carrying out this great and essential pre- 

 liminary survey, in the absence of which he did not pretend to say that the 

 line he had suggested was the best which could be chosen. 



Mr. G. Rennie, f.r.g.s., said that this was (to use the words of the President) 

 emphatically a water question ; for in the valley through which a canal would 

 have to pass, rain fell almost incessantly for nine months in the year, and such 

 rain was rarely seen in any other part of the world. It was therefore one of 

 the most important elements, or rather aliments, of the question. With regard 

 to the effect of admitting water into the canal either from the Pacific Ocean 

 or from the Atrato, he had no apprehensions ; for the length of the canal between 

 its junction with the Pacific at Paracuchici and with the Atrato was so great, 

 and the oscillation of the tide at either end so small (notwithstanding they 

 were high and low at different periods), that before the water of a spring tide 

 in the Pacific could have any efiect on the water in the canal, the velocity of 

 the water would be so retarded by the friction and resistance of the sides and 

 bottom of the canal, as to reduce the inclination of the surface of the water (in 

 the canal) to three inches per mile over the whole distance of the Truandcfpart ; 

 but before the water of the Pacific reached the farther extremity, the tide 

 would have fallen, and thus the two opposing forces of the pressure of the water 

 without, and the canal within, would be reduced to an equilibrium. At 3 inches 

 per mile, the motion of the water is scarcely perceptible. As regards the 

 effect of the passage of the water-flow of the Atrato, no fear need be enter- 

 tained ; the area of the section of the Atrato at the junction, being from nine 

 to ten times greater than that of the canal of the Truando, will afford an 

 abundant supply of water to the canal. The Atrato is as wide as the river 

 Thames at Waterloo Bridge, and 47 feet deep, so that there is ample width 

 and depth for the largest merchant vessels, and even vessels of war. The 

 objections to navigating it were considerable, as its channel was difficult to 

 define, when passing through the many lagoons or lakes which overflowed its 

 banks in many places, particularly at its junction with the Truando, which is 

 described by Mr. Kelley to be usually covered by a vast lagoon or lake at the 

 entrance, and thus very difficult to find ; so that the course of the river or 

 canal will have to be buoyed and staked, and pilots would be necessary. 

 With regard to the other parts of the canal there were difficulties of no 

 ordinary kind. The Truando was one of them. The entrance into the Gulf 

 of Darien was exposed to the N. and N. E. winds, but their effect did not 

 seem to influence the mouths of the Delta, behind which there was shelter. 

 It had been proposed to convert the Coquito branch into the main entrance 

 into the Atrato, by blocking up the branches and turning all their channels 

 into the Coquito. There were other difficulties at the entrance into the canal 

 from the Pacific, as at Paracuchici, where the surf beat strongly on the shore, 

 although the water was calm inside. It would be a question between an 

 entrance with an open mouth on that part of the shore, or into Humboldt Bay. 

 It would also be reasonable to put down- half a million as the cost of each 

 harbour, in addition to the cost of the canal, estimated at thirty millions, say 



