MR. J. PRESTWICH ON SUBMARINE TEMPERATURES. 
673 
Explanation of Sections. 
PLATES 66, 67, & 68. 
The position of the sections will be found on the Map, and the initials attached to 
the numbers have the same reference on both. 
In the absence of observations in the direct line of section some of those at a short 
distance on either side are included. 
The vertical lines indicate the position and depth of the temperature-soundings, 
and the figures in italics connected with them give the temperature at the surface and 
at depths in degrees of Fahrenheit. The other figures on the top line mark the degrees 
of latitude. The stronger figures in italics relate to the probable position of the bathy- 
metrical isotherms generally. 
The separate numbers at depths indicate the depth in feet to which soundings have 
been made in any latitude, the sign -j- showing that no bottom has been reached. 
All the observations used in the Sections have been subjected to correction for pres- 
sure, as adopted p. 612, viz. by making a deduction of 1° Fahr. for every 1700 feet 
of depth, exclusive of the observations of Lenz, Du Petit-Thouars (such of them as 
are given in parentheses in the Tables), Martins, Pullen (in part), and those of Eoss, 
Parry, and Sabine of 1818-19, which are taken, for reasons before given, as recorded 
by the original observers. It is possible that in some instances (as, for example, 
James Eoss) a larger correction might be necessary, and that in the Antarctic seas the 
isotherm of 35° F. should be replaced by one of 33° or 32°*; but this will not much 
affect the correction for the more numerous observations at lesser depths. 
All the depths are given, for the sake of uniformity, without correction for angle 
of rope, as that could only possibly be known in but few cases. The importance, how- 
ever, of a correction for this also will be evident by reference to the large allowances 
which Du Petit-Thouars f has often thought it necessary to make in his soundings, the 
corrected readings being given between parentheses. Only in 21 cases does he record 
“ the angle of the line from the vertical ” as 0 ; in the other 38 cases he found it to vary 
from 10° to 67°; and he estimated the difference caused by the latter extreme case as 
equal to a reduction of the observed depth of 5872 feet to a corrected depth of 2296 feet. 
The want of information on this point is one reason for taking, as we have done, a 
minimum correction for pressure. 
Where the observations are sufficiently numerous the bathymetrical isotherms are 
laid down in continuous lines. The dotted lines indicate the probable prolongation of 
the isotherms, on the supposition that there are no disturbing causes ; but it must be 
borne in mind that the isotherms (the lower ones especially) are liable to rise with every 
* Should some of the observations of the ‘ Challenger ’ be fonnd to correspond in position with any of those 
recorded in these pages, they will furnish a measure whereby to correct these or those of other observers. 
t See also the corrected depths of Lenz (ante, p. 599) and of Wauchope, 1816, and Sabine, 1822 (Tables). 
