2 
BULLETIN 1059, U. S. DEPARTMENT OF AGRICULTURE. 
Measurement of environmental eon- Page, 
ditions affecting vegetation — Con. 
Solar radiation — light — Contd. 
Apparatus and methods for 
radiant energy measure- 
ments — Continued. 
Spectroscopic measure- 
ments 56 
Spectro-photographs 57 
Spectro-bolometer 58 
Evaporimeters 58 
Instruments 59 
Precipitation — 60 
Exposure of gauges 60 
Snow depths 61 
Snow-scale readings 61 
Tabulation , 63 
Instruments 63 
Soil moisture and soil qualities- 66 
Osmosis as a factor in water 
absorption 66 
Problems and some definitions- 71 
Total moisture determinations 73 
Soil wells for representa- 
tive points 73 
Technique of periodic sam- 
pling 76 
Determination of non-avail- 
able moisture 79 
Direct determination of 
wilting coefficient 80 
Indirect methods for wilt- 
ing coefficient 84 
Capillary moisture 85 
Moisture equivalent 93 
Hygroscopic coefficient 97 
Calculation of the available 
moisture 100 
Availability of the moisture. 101 
Coefficient of availability.. 101 
Osmotic pressure in plant 
tissues sl03 
Method of determining 
freezing points 107 
Osmotic pressure in soils. 109 
Vapor transfer in soils. 109 
Vapor transfer method. 112 
Computing the coefficient- 120 
Other soil properties to be 
studied 121 
Acidity and alkilinity 121 
Hydrogen-ion concentra- 
tion 122 
Mechanical analysis of soils 123 
Determination of humus 126 
Loss on ignition 127 
Ammonia-soluble humus. 127 
Measurement of environmental con- Page, 
ditions affecting vegetation — Con. 
Soil moisture and soil qualities — 
Continued. 
Other soil properties to be 
studied — Continued. 
Capillary conductivity 128 
Chemical analyses for nu- 
trients 129 
Summary of soils discussion. 136 
Special equipment 142 
Atmospheric humidity 143 
Instruments 146 
Wind movement 146 
Instruments 150 
Evaporation 151 
Objects and nature of evapo- 
ration measurements 151 
Instrumental methods 154^ 
Free-water surface 154 
Measurement 154 
Nonfree-water surface 155 
Piche evaporimeter 155 
Porous cup atmometer 156 
Shive's nonabsorbent por- 
ous-cup atmometer 157 
Standardization 159 
Computation of field re- 
sults 159 
Exposure 160 
Forest Service evaporim- 
eters 16.1 
Observations 162 
Tabulation 163 
Directtranspirationmethod- 164 
Cobalt-chloride method 164 
Method of excised twigs. 165 
.Method of potted plants- 166 
Instruments 168 
Phenology 168 
External field observations 170 
Internal or physiological observa- 
tions 171 
Field observations, photographs, and 
maps 172 
Appendices 175 
A. Vapor pressure tables for ba- 
rometric pressure 21.42 
inches 175 
B. Osmotic pressures and freez- 
ing-point depressions : 198 
C. Titration methods for alka- 
linity and acidity 199 
Alkalinity test 199 
Acidity test 200 
List of references 202 
INTRODUCTION. 
OBJECT. 
Forestry, like 
or 
medicine, is largely an applied 
science. Its development is based on fundamental knowledge of the 
natural sciences. Knowledge of the tree itself is purely botanical 
