Earth Temperatures. . 67 



season (Mr. Symons, in a series of observations already quoted, 

 found the water of the lake in Eegent's Park to range in tem- 

 perature between 80° and 29° F.). I have arranged, in the form of 

 a diagram, the mean monthly temperatures of London water sup- 

 plies for the nine years 1884-1892, as given by Dr. Frankland in 

 the Registrar-General's Weekly Returns for those years. In this 

 diagram the temperature of the Kent Company's water, which is 

 drawn from deep wells in the chalk, is represented by a dotted line, 

 and the average temperatures of the water of the companies 

 deriving their supply from the Thames by a thick line. These 

 temperatures, however, are those of the water as drawn from the 

 mains, and do not represent it as delivered to consumers, for in 

 its passage through the smaller branches of the system the water 

 will doubtless have to a considerable extent approximated its 

 temperature to that of the soil in which the pipes are laid. Still 

 the difference in temperature between the deep-well water of the 

 Croydon Corporation and the Thames water of the Lambeth 

 Company is, I find, sufficiently perceptible when one takes one's 

 morning tub, the former being comparatively equable in tempera- 

 ture, the latter icy cold in winter and lukewarm in summer. 



The water of deep springs, such as those which issue from the 

 chalk at Waddon, is similarly equable in temperature, having 

 about the mean temperature of the year ; hence it feels de- 

 liciously cool in summer, while it steams on a frosty day, and 

 keeps aquatic plants in verdant growth all through the winter. 



When the temperature of the earth at depths below that at 

 which the influence of the seasons ceases can be ascertained, as 

 in mines, deep wells and borings, and tunnels, it is found to 

 increase steadily with the depth, though the rate of increase 

 varies considerably in different places. The Underground Tem- 

 peratures Committee of the British Association made, in 1882, a 

 report, giving a summary of the best observations which had 

 been made up to that date. In thirty-six such observations 

 quoted the rate of increase of temperatui'e with the depth varied 

 from 1° F. in 130 ft. in a deep well at Liverpool, to 1° F. in 

 34 ft. in a mine in Weardale. The rate of increase, however, 

 was usually similar in observations made in the same neighboui-- 

 hood ; thus, in artesian wells in the neighbourhood of London 

 and Paris it was 1° in about 56 ft. ; in the deep collieries of the 

 coalfield east of Manchester it was 1° in 77 ft. The differences 

 in the rates of increase in different cases may partly be explained 

 by differences in the nature of the rocks or configuration of the 

 surface. In compact rocks the heat conductivity is greater, and 

 the increase of temperature with depth consequently slower than 

 in looser and softer beds. Again, in laminated rocks the heat 

 conductivity is greater in the direction of the layers than across 

 them; hence in stratified rocks dipping at a high angle, the 



