674 
ME. J. PEESTWICH ON STJBMAEINE TEMPEEATUEES. 
important irregularity (banks, shoals, &c.) in the bed of the ocean, and the upper 
isotherms may be variously deflected by surface-drifts and currents. 
It is probable that in some of these Sections (as, for example, in the North Pacific, 
Sect. 4, and in the South Atlantic, Sects. 1 & 2) the irregularities of curvature may be 
exaggerated, owing to the want of uniformity in the instruments used by the different 
observers, and by the necessity of using a general correction for all. 
Very little was known before 1868 of the deep bed of the Atlantic. The few indi- 
cations of the ocean-bed given in the sections are taken from notices in the several 
voyages above recorded and from Maury. In the higher north latitudes we have the 
soundings of Ross, Kane, Scoresby, and Martins. In section No. 2 the greater depths 
of Scoresby are in the sea west of Spitzbergen, and the lesser ones of Martins between 
Spitzbergen and Norway, which accounts for the break in continuity of depth. 
The position of the bathymetrical isotherms and the indications of the sea-bed are 
confined strictly to observations anterior to 1868. 
