TEMPERATURE 



69 



Readings 



99. Time. The hourly and daily fluctations of the temperature of the 

 air render frequent readings desirable. It is this variation, indeed, which 

 makes single readings, or even series of them, inconclusive, and renders 

 the use of a recording instrument almost imperative in the base station at 

 least. Undoubtedly, a set of simultaneous readings at different heights in 

 one station, or at the same height in different stations, especially if made 

 at the maximum, have much value for comparison, but their full significance 

 is seen only when they are referred to a continuous base record. Such 

 series, moreover, furnish good results for purposes of instruction. In re- 



Fig. 21. Richard thermograph. 



search work, however, it has been found imperative to have thermographs 

 in habitats of widely different character. With these as bases, it is possible 

 to eke them out with considerable satisfaction by means of maximum- 

 minimum thermometers in less different habitats, or in different parts of 

 the same habitat. Naturally these are less satisfactory, and are used only 

 when expense sets a limit to the number of thermographs. In a careful 

 analysis of a single habitat, more can be gained by one base thermograph 

 supplemented by three pairs of maximum-minimum thermometers in dissimi- 

 lar areas of the habitat than by two thermographs, and the cost is the 

 same. 



