THE WATER OF THE HABITAT 33 



vent a change in temperature, and are used only on the day they 

 are made. Light readings are of course necessary only when 

 one or more stations are shaded. For the sake of convenience 

 and accuracy, factors are always determined in the same 

 order, viz., temperature, humidity, wind, light; and the same 

 is true of the various points or levels, e.g., IJ meters, surface, 

 and soil. 



44. Point and hour readings. Readings taken as above at 

 the same point in the stations of a series are said to be made at 

 the same level, as the IJ-meter level, the surface level, etc. 

 Readings may also be taken simultaneously through the different 

 points of a single station. In this work, the observers are grouped 

 in each station in such fashion that they do not interfere with 

 the correct reading of each instrument. Such determinations are 

 most valuable in the case of temperature, which shows greater 

 differences at the various levels. Important differences of 

 humidity and wind are also discovered, and, in layered formations, 

 marked variations in the amount of light. Series of this sort 

 are likewise read upon signal. Hour series are indispensable for 

 obtaining the variation of each factor during the day. They 

 are read for each level upon signal in the manner already indi- 

 cated, but the series is repeated every hour throughout the day. 

 The number and position of the levels in all of the different series 

 are properly determined by the character of the vegetation. In 

 general, there should be levels corresponding to the surface, to 

 the height of the herbaceous vegetation, and an air level above 

 the latter. For temperature, one or two soil levels are necessary 

 also. 



45. Records. A definite form of field record saves much 

 time and prevents many mistakes. Printed blanks of the form 

 indicated below, 7fx9| inches in size, have been found to be 

 the most satisfactory. Each blank suffices for recording two 

 full sets of readings through ten stations. The details may of 

 course be modified as seems desirable. The blanks arc carried in 

 a cover protected with oil-cloth. The field readings are entered 

 directly in ink in the case of temperatm-e and wind, while liglit. 

 humidity, and water content are recorded only when the final 

 results are obtained, field memoranda being employed for the 

 direct readings. 



