573 
of Edinburgh, Session 1868-69. 
tine Confederation, through Catamarca and Santiago at its furthest 
north, returning thence perhaps outside the east coast. 
The central and eastern parts of Patagonia have the highest 
range in the southern hemisphere, and this does not exceed 40°; 
observations at Mendoza in the north giving only 38° of range. 
The lines of equal yearly temperature over the globe, or the 
annual isotherm^, are sometimes termed “ climate lines,” and one 
is very apt to imagine that every place which lies under the same 
isotherm has the same climate, which is by no means the case. 
With a view to showing the variation of range in those parts of the 
earth which have the same mean annual temperature, six of the 
annual isotherms have been opened out, as it were, on each side of 
the meridian of Greenwich, and the amount of range for each point 
of these lines has been projected vertically above it, giving remark- 
able curves, of which the one shown beneath the chart of the annual 
isotherms* which accompanies this paper is a sample. 
On the isotherm of 10° in the northern hemisphere, it is observed 
that the range may vary from 30° in the Arctic Ocean to above 100° 
in Eastern Siberia, near Yakutsk. The mean range on this iso- 
therm is 65°. 
The isotherm of 20° has also a mean range of 65°, but may have 
as little as 25° in the Arctic Ocean, and as much as 100° in Asia. 
On the isotherm of 30°, or nearly a mean annual temperature of 
the freezing point, the range may vary from below 20° between 
Greenland and Norway, to above 90° in Eastern Asia, the mean 
range on this line being 60°. 
The isotherm of 40° shows a variation of range of from less than 
20° in the Atlantic Ocean south of Iceland and in the North Pacific, 
to above 80° in Mongolia; whilst the mean range is 47°. 
The line of 50° of mean annual temperature has a mean range of 
41° ; but this varies between 20° in the west of Ireland, to above 
80° in Asia. 
On the isotherm of 60° we find a mean range of 40°, but only 10° 
in the Pacific, and above 70° in Central Asia. 
From these curves then, it is evident that hardly any two regions 
* The annual isothermal lines shown on this chart are those of Dove, re- 
cently revised by Mr Buchan. 
