OBJECTS AND METHODS. 37 



might be called the method of parallel stations. This is a commendahle 

 arrangemeut, and promises the speedier results, the more the climate 

 at the station takes on a continental character. The distance of the 

 stations of each pair from each other is an important point. In each 

 pair the meteorological elements should be taken at the ordinary height 

 and also in the tree crown. The temperature of trees and soil should 

 be included. As to precipitation, it is of importance to get not only 

 the amount which passes through the foliage, but also that which runs 

 down the trunk. The penetration of precipitation into the soil, the 

 evaporation from the surface in different kinds of forests and with 

 different coverings of the soil are of importance because the state of 

 humidity and temperature deiiends on them. Observations of ozone at 

 different heights are contingently recommended. These observations 

 should be exactly duplicated, so far as possible, at the held stations. 

 The treetop observations should be dui)licated by field observations at 

 the same height. To get the influence of the forests on their vicinity, 

 a different system of stations is desirable; this should be a system of 

 radial stations as contradistinguished from the parallel system. This 

 consists of one station in the forest and several outside, arranged in 

 the directions of the four principal points of the compass. There should 

 be at least two in each direction and at different distances from the 

 forest, so that one set should include at least nine stations. All the 

 observations carried on at the parallel stations should also be taken at 

 the forest station of the radial system, but at the field stations the 

 number of instruments may be reduced to a psychrometer, evaporome- 

 ter (Piche's), and a rain gauge, and the observations at the height of 

 the tree crown may be omitted. 



The question of exposure of thermometers aroused much discussion 

 and it was agreed that comparative observations should be under- 

 taken. As to hours of observation. Dr. Miittrich favored morning and 

 noon (2 p. m.), while M. Grandeau and Dr. Ebermayer favored morning 

 and evening hours. Dr. Eiegler thought the 2 ]). m. observation was 

 to be especially recommended because it was about the hour of maxi- 

 mum forest effect. The conference finally decided to recommend 

 morning and evening hours, with the reading of maximum and mini- 

 mum thermometers. Observations of insolation were discussed, but 

 MM. Mascart and Tacchini assured the conference that no suitable 

 actinometer exists. It Avas, therefore, decided that observations should 

 at first be undertaken only on the time, dnration, and relative inten- 

 sity of sunshine; the latter on sensitive paper, at stations of the first 

 order. The subject of an actinometer capable of giving insolation tem- 

 peratures with exactness was recommended as a subject worthy of the 

 especial attention of scientific institutions. 



It w^as decided that soil temperatures should be taken at various 

 depths up to inches (1 mm). The humidity should be obtained by 

 the means of August's psychrometer and a hair hygrometer, and tri- 



