eee jo ee 
Barometric Anomalies about the Andes. 387 
the head of uninterrupted navigation, down to the sea, is 8 inches 
to the mile. Eight inches to the mile is probably tog great a de- 
scent from the foot of the last rapid in the Amazon to the sea, 
But the object of the diagram is not to illustrate the slope of the 
Amazonian water-shed ; it is to illustrate the remarkable degree 
of barometric pressure that has been found near the eastern base 
of the Cordilleras. I therefore assume the descent of the river to 
be on the average, very nearly what Herndon’s observations made 
It to be, after he had passed from under the supposed elevation, 
_ orridge of the atmosphere. The distance from Chasuta to the 
sea is, by the windings of the river, about 3,285 miles. 
The dotted line, showsa profile view of Herndon’s descent, 
according to the temperature of the boiling point; and the con- 
tinuous line, his actual descent, upon the supposition that the 
average inclination of the river from Chasuta to the sea is as be- 
fore stated—8 inches to the mile. 
_ Hrom Nauta, where his boiling point placed him at only 126 
feet above the level of the sea, to Egas, where, though drifting 
down the stream all the way, it placed him 1,715 feet above it, 
the distance is 707 miles. If intermediate observations could 
have been made between these two places, he would probably 
have found that he had passed from under this supposed air-cast 
range of mountains long before he reached Egas. __ 
However, observations sufficient for a full explanation of the 
phenomena presented by this diagram are wanting, and we must 
| with those we have, as best we may, hoping by calling at- 
tention to the subject upon such meagre facts, some other trav- 
eller will be provoked into a thorough and complete series of baro- 
metric observations along the slopes of the Andes. 
Lieut. Herndon assumed that at the mouth of the Amazon, 
the mean height of the barometer would be 30 in., the boiling 
point 212°. But during a portion of his descent, the belt of the 
equatorial calms was over the mouth of the Amazon. All the 
ships whose Log Books I have with records in them, as to the 
rometer, show that it does not stand as high in these calms as 
it does on either side of them. Dewey’s observations at Para, 
confirm this. Therefore Herndon’s heights as determined by 
the boiling point of water during his descent of the Amazon, are 
probably not so great as the standard, to which he referred his ob- 
servations, would make them. At any rate, whether his observa- 
tions were uniformly too great or too small, is immaterial to ou, 
present purpose, which is to show the remarkable openers “a 
covered by him in the pressute of the atmosphere, particularly 
ing his nt of the Amazon. 
At aig dl which is about 2,700 ines'ahorve the mouth 
of the Amazon, it I lation of atmosphere 
sufficient to cause a pressure nearly equal to the ordinary atmos- 
