PROFESSOR FORBES ON THE TEMPERATURE OF THE EARTH. 



207 



powEE OF THE DIFFERENT SOILS OR ROCKS FOR HEAT is Very palpable. But to 

 submit it to numerical calculation, a more elaborate analysis is necessary. Each 

 year has been lii'st considered by itself, and then the whole united. 



C. Thermometric Ranges. 



To ascertain the range for each year, the maximum and minimum points of 

 the curves of each thermometer were ascertained graphically by the aid of an 

 elastic wire, bent so as to represent a curve which should pass through the zig- 

 zags of the temperature curve, and connect the observed points with tolerable 

 accuracy. The points of greatest and least temperature in each year were thus 

 represented with a certain degree of approximation, and the results are shewn in 

 the following table. 



Table VIII. Shewing the Maximum and Minimum Temperatuee and Range 



FOR each of Five Years. 



Theory shews, that the annual range ought to decrease in geometrical pro- 

 gression, as the depths increase uniformly. In other words, the ranges may be 

 represented by the ordinates of a logarithmic curve. And that such is the case 

 may be seen from the curves in Plates IX. and X., where the logarithmic curves 

 are drawn through points so as to represent, as well as is practicable, the law of 

 decreasing range at the different stations. These diagrams were constructed with- 

 out any reference to one another ; and their general coincidence is highly satis- 

 factory. 



