84 FOREST INFLUENCES. 



over a plain distant from woods. The forest-field or forest-glade sta- 

 tion is, therefore, not exactly like a station in an open plain. It is 

 likely to average a little warmer in the day and a little cooler at night, 

 giving it a greater daily amplitude not only than that under trees, but 

 greater, too, than that in open prairies. Whether the mean temper- 

 ature would be diflterent in the forest-field station would depend on the 

 relative increase in maximum and minimum. If the increase in the 

 former is greater, the forest-field station temperature would be higher 

 than that of the prairie station j if the minima exaggeration is greater, 

 it would be the opposite. 



The phenomena mentioned above are especially noteworthy in forest 

 glades. The horizontal reflection from the foliage comes there from all 

 sides, and the heat rays not absorbed are reflected from the opposite 

 side, a part to the sky, a part to the opposite side, and this reverbera- 

 tion of the heat makes such places oppressively hot in the early after- 

 noon. This is well known to tlie hunter and to the pioneer with his 

 little clearing in the deep woods. Again, as the closed glade is in the 

 lee for winds from all directions, the air is always somewhat stagnant 

 and clear weather celestial radiation nuTst always make a lower mini- 

 mum temperature than where there is free circulation of air. The field 

 station, when there is a i^air, one in the forest, the other near by in 

 the field, must always have something of the glade character in its 

 temperatures, and the data given at this point must be somewhat af 

 fected by it. The relations for range of temperature, as between the 

 interior forest and its external station should show this, and the ranges 

 should be somewhat greater than between forest and plain. Whether 

 there is an exaggeration of the mean values of W—0 can only be told 

 by observation. Fortunately the plan of the Swedish observations 

 included and was rather devoted to this particular side of the problem. 

 The stations were really of four kinds. The first were under woods, of 

 which there were but three. The second were the parallel field stations 

 for the three forest stations. These were usually located in an '' endroit 

 libre" (opening), but the distance of the forest in all directions is given, ' 

 so that this means a " glade"' of greater or less size. The third class 

 were stations in "clairiere" (clearing), with the distance from woods in j 

 all directions (and not very great). Each of these also signifles a 

 "glade," but large and unlike the preceding. It has no corresponding 

 forest station. The fourth class comprises stations in largeoi^en places, 

 far from forests. These are stations in the plain. This distribution of 

 stations attbrds the great advantage of permitting a study of the aver- 

 age amount of change due to the "glade" positionof a station and thus 

 enabling us to pass from therelations between ])arallel stations to those 

 between wooded and treeless districts. It has, however, the disad- 

 vantage that the stations are not strictly comparable, as in the " par- 

 allel " system, and as would be the case in the " radial " system. This 

 difficulty can be in large i)art overcome by the careful selections of 



