114 



SGIENGE. 



[N. S. Vol. VII. No. 161. 



the statistical records of the extent and fre- 

 quency of the changes of the various atmos- 

 pheric phenomena. 



Climatology is a function of these phe- 

 nomena and should be expressed in terms 

 of the development of organic life. Climatic 

 changes produce, in many ways, more ap- 

 parent changes in plants than in animals, 

 and they should be taken as the standard 

 in the interpretation of our meteorological 

 data. Many plants are far more sensitive 

 in recording climatic changes than our 

 meteorological instruments. There are 

 localities where the character of th« leaf 

 or the peculiar excellence of the fruit pro- 

 duced show peculiarities in the climate 

 wlaich the instruments fail altogether to re- 

 cord, or rather which we have never yet 

 been able to deduce from the ordinary 

 meteorological records. The development 

 of plant life should, therefore, be taken as 

 the standard with which our instruments 

 should be compared and our methods ad- 

 justed in order that the elements of clima- 

 tology may be worked out from our meteor- 

 ological records. 



Climatology is not a simple summation, 

 but a complicated expression involving the 

 general relation of certain functions of 

 meteorological elements, the values of 

 which we do not as yet understand. The 

 principal elements influencing the economy 

 of plant life are temperature, humidity, 

 wind velocity, water supply and sunshine. 

 "Within certain limits the activities of the 

 plant are dependent upon the relation be- 

 tween these elements. Thus temperature 

 causes evaporation, the relative humidity 

 and the velocity of the wind control evap- 

 oration, while the moistui-e supply in the 

 soil provides the plant with water to re- 

 place that lost by evaporation. The influ- 

 ence of all depends upon the total intensity 

 of the sunshine. 



The rainfall, although a very important 

 meteorological element and of great eco- 



nomic and commercial importance, is not 

 considered a factor in climatology, as it is 

 not the immediate source of the water sup- 

 ply of plants. The soil is the receptacle of 

 the rainfall and, through the resistance it 

 offers to the descent of water and through 

 capillary action, maintains the water at the 

 disposal of plants. Hence the moisture 

 content of a soil is an essential factor in 

 climatology. Furthermore, as the soils in 

 the same field may differ greatly in their 

 power to retain water, we may have very 

 different climates over very small areas. 

 With forty inches of annual rainfall the soil 

 may be so open and porous and retain so 

 little moisture that the conditions may be 

 truly arid. We have small areas of truly 

 desert lands in our Eastern States. On the 

 other hand, with only eight or nine inches 

 of annual rainfall there are some soils so 

 retentive of moisture that they will produce 

 good crops with careful and thorough culti- 

 vation. 



The general relation of these elements 

 may be expressed in very general terms in 

 the following equation : 



/Temp. X wind veloR.\ Const, condition 



\Humid. X soil moist./ of plant growth. 

 Tliis is but an expression of facts perfectly 

 well known to greenhouse men. It will be 

 seen from this that to maintain constant 

 conditions of growth any marked change in 

 one of the elements must be followed by a 

 change in one or the other of the remain- 

 ing elements. Thus, if the temperature 

 rises, the wind must fall or the humidity or 

 soil moisture increase. If the humidity in- 

 creases, the temperature or wind velocity 

 should increase or the soil moisture should 

 decrease. The sunshine should be recorded 

 by the total intensity rather than by the du- 

 ration. If the intensity should decrease, the 

 other elements should all be lowered and 

 vice versa. If the above equation holds, it 

 appears that the change in either the hu- 

 midity or soil moisture or both must be 



