28 



PHYSICAL GEOGRAPHY OF BRITAIN. 



The estimate of 70 yards gives a temperature below 28° 

 for the summits of our highest mountains ; that of 80 

 yards makes it 30°. Now, as these summits do not attain 

 the line of perpetual snow, it is not unlikely that 30° may 

 prove a closer approximation than 27^°. Were we to 

 take the rate of decrease indicated by Lead Hills, say 

 120 yards, instead of 30° we should have 36° of tem- 

 perature. Our loftiest summits are too near the snow- 

 line for such an assumption. I believe to have heard 

 Professor Jameson state in his Lectures, that 90 yards of 

 ascent depresses the thermometer one degree. This scale 

 would give 32° of temperature for our highest summits. 



The mean annual temperature of the earth below 100 

 yards in Britain is almost the same as that of the air ; 

 but as we ascend the mountains it decreases more slowly. 

 The temperature of the earth is usually determined by 

 that of spring waters, but a distinction ought always to 

 be taken between those of variable and those of fixed 

 temperature. A spring changing its temperature with 

 the seasons (as all do when flowing some distance near 

 the surface, or collected into wells,) gives a higher mean 

 than one keeping almost the same temperature through 

 the year. Observations once a month are sufficient for a 

 good spring. The following are recorded : — 



TEMPERATURE OF THE EARTH IN BRITAIN. 





Alt. 



Temp. 



Place. 



Alt. 



Temp. 



Gosport 





52° 



Jesmond 



200 



45|°- 



Barnstaple 





52§ 



Newcastle 



180 



49 



Ditto 





50± 



Lead Hills - 



1280 



44 



Ditton - - 





54h 



Leith 





47f 



Crumpsall 



292 



48f 



Edinburgh - 



214 



47$ 



Kendal 





47£ 



Ditto 



230 



47 



Helvellyn 



2750 



41 



Ditto 



367 



47* 



Keswick 



250 



46§ 



Rose Bank - 



130 



*H 



