XI 
SAN CARLOS 
353 
great journey, which Spruce was unable to carry- 
out, and they will be also useful to geographers 
as supplementing what Spruce was able to perform 
in the exploration of this almost unknown region. 
I therefore think it right to give it here ; but as 
it is mainly of interest to the geographer, it is 
printed in smaller type.] 
To Sir William Hooker 
San Carlos, 27, 1853. 
I mark every day the maximum and minimum of the baro- 
meter, and it is interesting to observe with what regularity the 
atmospheric tides recur on the Equator, being apparently totally 
uninfluenced by changes in the weather. During the space of 
nearly two years, it has only twice occurred that the minimum 
has been considerably retarded beyond its usual hour, which is 
from 3 to 4 o'clock, while the maximum is attained between 
9 and 10. 
Ever since I have been on the Rio Negro I have made inquiries 
respecting the position and possible means of reaching the sources 
of the Orinoco, without any expectation, however, on my part of 
being able to solve this interesting geographical problem. Quite 
unexpectedly, the means of doing it seem about placed within my 
grasp. We were lately visited at San Carlos by the Comisario 
General of the Canton of the Rio Negro, Don Gregorio Diaz, who 
resides at San Fernando de Atabapo ; and on my mentioning to 
him how much I should like to reach the head-waters of the 
Orinoco, he at once entered ardently into the project, saying that 
it was what he had all his life been longing to do, and that if I 
would promise to accompany him he would arrange as many men 
well-armed as he could, to start on the expedition early in the 
year 1854. Nearly all the whites in the Canton seem eager to 
join us, being possessed with the idea that there is certainly an 
El Dorado at the source of the Orinoco. Don Gregorio is at 
present making a progress through his dominions, having come to 
San Carlos by the Atabapo and Guainia, and returning by the 
Casiquiari and Orinoco. He proposes to ascend above Esmeralda 
as far as the mouth of the Manaca, and to enter three days' 
journey within this river, where is a pueblo established a few years 
ago. He engages to make everywhere inquiries as to the best 
route for reaching the sources of the Orinoco, and the facilities or 
hindrances we may expect to encounter. I heard from him the 
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