156 On an Isothermal Oceanic Chart, illustrating 
rest of the Atlantic and the other oceans we have employed the 
Meteorological volume of Captain Wilkes of the Exploring Ex- 
pedition Reports, which embraces observations in all the oceans 
and valuable deductions therefrom; also, the records of other 
travellers, as Humboldt, Duperey of the Coquille, D’Urville of the 
Astrolabe, Kotzebue, Beechey, Fitzroy, Vaillant of the Bonite, 
Ross in his Antarctic Voyage, together with such isolated tables 
as have been met with in different Journals. 'The lines we have 
laid down, are not however, those of any chart previously con- 
structed, for the reason stated, that they mark the positions where 
a given temperature is the mean of the coldest month (or coldest 
thirty consecutive days) of the year, instead of those where this 
temperature is the mean annual or monthly heat; and hence, the 
apparent discrepancies, which may be observed, on comparing 
it with isothermal charts. 
The isocrymal lines adopted for the chart are those of 80°, 74°, 
68°, 62°, 56°, 50°, 44°, and 35° of Fahrenheit. The tempera- 
re. 
the Hawaiian Islands and the Feejees; and as the temperature at 
* In the author's Report on Geology, 66° F. is set do the limiti ipera- 
ture of Coral-reef Seas ; this, howeree, is gic as Feighebeeleny rig ar em 
to be the mean of the coldest month, and is therefore here used. 
