36 FOREST INFLUENCES. 



(5) Evaporation within and without the woods. 



(6) The rain and snow reaching the ground within and without the woods. 



(7) The temperatures of forest soil at the surface and at the depths of 6 inches, 

 1,2,3, and 4 feet, compared with the temperatures at corresponding depths in the 

 open fields. 



There were also the highly important conditions attached that the 

 instruments and their disposition should be alike, and that the hours 

 of observation and methods of reduction should be the s'ame. 



In the second international meteorological congress, held at Rome 

 in April, 1879, it was resolved that — 



In order to contribute to the progress of forest and agricultural meteorology, the 

 congress recommends as a programme of study : 



(1) The influence of the meteorological elements upon vegetation. 



(2) The inverse influence of vegetation upon the meteorological elements. 



(3) Agricultural warnings. 



The congress, finding the subject too important to treat hastily, con- 

 cluded to charge the international committee with the convening of a 

 special international conference to take into consideration the develop- 

 ment of agricultural and forest meteorology. 



Such a conference convened at Vienna on the 6th of September, 

 1880. This was so representative a meeting and illustrated so well 

 what the most able and most experienced men thought on this sub- 

 ject that the reports, remarks, and resoluticms will be given at some 

 length so far as they relate to the action of forests on climate. Dr. 

 Lorenz-Liburnau, of the Austrian Department of Agriculture, and 

 president of the conference, said that when the influence of vegetation 

 ou climate was referred to, solitary plants could not be meant. It was 

 a question of masses of vegetation, such as meadows, moors, and forests. 

 There was also a distinction to be made between the climatic action 

 produced within the massed vegetation and that upon the vicinity. It 

 is only for a forest that the question oftlie interior climatic action can 

 arise, and on this question certain definite numerical results had been 

 obtained for central Europe, in certain localities. These show that 

 the inner temperatures are slightly lowered, the temperature extremes 

 are moderated, the relative humidity is raised, and the evaporation 

 diminished, while it remains doubtful whether the absolute humidity 

 or the frequency or quantity of precipitation are changed. 



As to the influence of vegetation on its vicinity, exact data do not 

 exist, either for the forest or for other forms of vegetation in mass. 

 Yet, ou theoretical grounds, it can not be doubted that such an intlu 

 ence exists, within certain limits, and appropriate methods of observa- 

 tion must be able to show it. They should include observations on the 

 temperature, precipitation, cloudiness, insolation, and wind. The con- 

 ference adopted these views. 



As to the method of observation, Dr. Liburnau ])ointed out that the 

 existing arrangement of one station within and a station for compari- 

 son outside the region covered by the vegetation to be investigated 



