[ 59 ] 
II. Account of Levellings carried across the Isthmus of Panama, to ascertain 
the relative height of the Pacific Ocean at Panama and of the Atlantic at the 
mouth of the river Chagres ; accompanied by Geographical and Topographical 
Notices of the Isthmus. By John Augustus Lloyd, Esq. Communicated 
by Captain Sabine, Secretary of the Royal Society. 
Read November 26, 1829. 
In November 1827 I received a special commission from General Bolivar 
to make a survey of the Isthmus of Panama and Darien, in order to ascertain 
the best and most eligible line for a communication (whether by road or canal) 
between the two seas. On my arrival in Panama in March 1828 I was joined 
by a brother officer of Engineers, a Swede in the Colombian service, a good 
mathematician and of habits of great correctness in observation. 
Upon consulting together, we found that we could combine the particular 
object of the commission with a second object in which we both felt a deep inter- 
est, namely, the determination of the relative height of the ocean on either side 
of the Isthmus ; and that we could best accomplish both, by taking a part of 
the present line of road between Porto Velo and Panama, until we should fall 
in with the river Chagres about twenty miles above Cruces, which village is 
the usual landing-place for all articles of commerce in their transit from the 
North Sea to Panama. 
To avoid delay, we commenced our operations on the 5th of May, although 
the rainy season had for some days set in ; being resolved to overlook the 
absence of personal comfort, the unhealthiness of the season to a European 
constitution, the inadequacy of our means, and various other difficulties 
unnecessary to enumerate, as we finally succeeded in surmounting them. 
The instruments used for the levelling were, — A 20-inch spirit level of 
Carey’s best construction, with extra telescopes, levels, shade tubes, &c., which 
I received from the museum at Bogota ; a pair of excellent station staves 
made by Harris and graduated as usual, with vernier scales added by myself 
to read off to thousandths of a foot when required ; Gunter’s chains ; an 
i 2 
