ILLUSTRATIONS (18). ISTHMUS OF PANAMA. 435 



an equatorial degree) or 16 to 20 English geographical miles. 

 On the Pacific coast also, the deep Golfo de San Miguel, into 

 which falls the Rio Tuyra, with its tributary the river Chu- 

 chunque (Chucunaque), runs far into the Isthmus. The river 

 Chuchunque too, in the upper part of its course, runs within 

 16 geographical miles of the Antillean shore of the Isthmus, 

 westward of Cape Tiburon. For upwards of twenty years 

 I have been repeatedly consulted on the problem of the Isthmus 

 of Panama, by companies having ample pecuniary means at 

 their disposal ; but in no instance has the simple advice I 

 have given been followed. Every engineer who has been 

 scientifically educated knows the fact that between the tro- 

 pics, even without corresponding observations, good baro- 

 metrical measurements (horary variations being taken into 

 account) may be relied on as correct, within from 75 to 96 

 feet. Besides it would be easy to establish, for the space of a 

 few months, one on each shore, two fixed barometric stations ; 

 and frequently to compare the portable instruments used in 

 the preliminary levelling with each other, and with those at 

 the fixed stations. The point demanding the most atten- 

 tive examination is that where the range of mountains 

 between the Isthmus and the main continent of South America 

 sinks into hills. Considering the importance of this subject 

 to the commercial interests of the whole world, the examina- 

 tion should not, as heretofore, be restricted within narrow 

 bounds. A complete comprehensive survey, including the 

 whole eastern part of the Isthmus — the results of which would 

 be alike useful in facilitating every possible scheme, whether 

 of canals or railroads — can alone decide the much discussed 

 problem, either affirmatively or negatively. This work will 

 in the end be undertaken, but had my advice been adopted, 

 it would have been done at first. 



(19) p. 418 — "Impressions excited by the accidental circum- 



stances of life" 



In Cosmos I have adverted to the incitements to the Study 

 of Nature. (Vol. ii. p. 371, Bonn's edition.) 



(20) p. 420 — " Of importance in determining the longitude of 



Lima." 



At the time of my expedition the longitude of Lima, 



2 f 2 



