NOMOS. 133 



face. At the depth of 25 feet, for example, this in- 

 terval is full six months, and the result is that the 

 mean temperature of January is manifested in July, 

 and the temperature of July in January. These are 

 the facts, and what is their significancy ? Do they 

 show that the heat of the sun is not transmitted be- 

 yond a certain very limited depth below the surface 

 of the earth? Assuredly not. On the contrary, 

 the fact that the heat travels so slowly as to be six 

 months in reaching the depth of 25 feet is sufficient 

 to show that it may travel indefinitely further with- 

 out giving any sign of its presence by fluctuations in 

 its intensity. It is sufficient to show this, for after 

 the end of six months the earth changes its relations 

 to the sun, and the process of giving up heat from 

 the parts deeper than 25 feet must be changed for 

 that of receiving heat, and, vice versa, the process of 

 receiving must be changed for that of giving up. 



There are also other and better reasons for sup- 

 posing that the heat of the sun may and actually 

 does penetrate below the stratum of invariable tem- 

 perature, and these are to be found in the previous 

 considerations respecting the nature of heat. What 

 is heat ? Heat, according to the premises, is a sign 

 of a current travelling under difficulties. If the 

 current be made to pass through a chain consisting 

 of alternate links of thick copper wire and fine pla- 

 tinum wire, the platinum links are alone heated, 

 because they are not fully adequate to the convey- 

 ance of the current (see p. 89). According to the 

 premises, indeed, the fact that the heat of the sun is 

 only perceptible at a certain depth below the surface 



K 3 



