HYDROGRAPHIC REPORTS. 85 
the war, by Lieuts. Alden, Blunt, and May, of the U. S. Navy, 
and which you directed me to assume as correct, shows that this 
depth may be carried as far as their examinations went. The 
present survey resumes the work where they stopped, and 
extends to the rapids of Suchil, on the Coatzacoalcos River, and 
to stake No. 47 of the railroad "pieadura" on the left bank of 
the Rio Jaltepec. 
This work has been done as you directed, and in the following 
manner : 
The course of the river was determined by compass-bearings 
of points upon its banks, taken successively as the work pro- 
gressed, and usually with the greatest ranges afforded by the 
bends of the river. The distances between these points were 
measured by Massey's patent log. By graduating the one-mile 
circle of this instrument to every five-hunclredths, these dis- 
tances were easily read to the nearest one-hundredth of a mile ; 
and by measuring the strength of the current with an ordinary 
log-reel, and noting the time occupied in running from one sta- 
tion to another, the corrections for current could be determined 
and applied to the reading. But as it was always necessary to 
return over the same ground, the distances were measured and 
the elapsed times noted both ways, and the correction for cur- 
rent proportioned from these data : thus any error arising from 
an inequality of the current in the bends and reaches has been 
avoided. At the same time a sketch-book was taken in the boat, 
and an outline of the banks of the river, embracing the topog- 
raphy so far as it was visible or easy of access, was made as 
an illustration of the notes. 
The line of deepest soundings, as laid down upon the chart, 
was run for the most part by the eye and judgment, inasmuch 
as the channel may easily be traced from the appearance of the 
banks, and from the general law in all rivers, of following the 
bends. It did not, therefore, seem advisable to waste time in 
zigzagging the whole river, but wherever there was room for a 
doubt as to the precise locality of the deepest channel, or when- 
ever shoaler water was found than had been met with below, a 
careful and minute examination was made ; and even without 
these causes operating, cross-sections of the river were frequent- 
