68 



THE HABITAT 



are communicated to a hand carrying a pen. The latter traces a Hne on the 

 record sheet which is attached to a metal disk made to revolve by an eight- 

 day clock. In practice the thermograph is set up in the shelter which con- 

 tains the psychrograph, and in exactly the same manner. The clock is 

 wound, the record put in place, and the pen inked in the same way also. 

 The proper position of the pen is determined by making a careful ther- 

 mometer reading under the 

 shelter, and then regulat- 

 ing the pen-hand by means 

 of the screws at the base 

 of it. A similar test read- 

 ing is also made each 

 week, when the clock is re- 

 wound. A record sheet 

 may be left in position for 

 three weeks, the pen being 

 filled each week with a dif- 

 ferent ink. The fixed or- 

 der of using the inks is red, 

 blue, and green as already 

 indicated. 



Owing to the fact that 

 they are practically station- 

 ary, soil thermographs are 

 of slight value, except at 

 base stations. Here, the 

 facts that they are expen- 

 sive, that the soil tempera- 

 tures are of relatively lit- 

 tle importance, and that 

 they can be determined as 

 easily, or nearly so, by simple thermometers, make the use of such instru- 

 ments altogether unnecessary, if not, indeed, undesirable. In a perfectly 

 equipped research station, they undoubtedly have their use, but at ordinary 

 stations, and in the case of private investigators, their value is in no wise 

 commensurate with their cost. 



Fig. 20. Shelter for thermograph. 



