AIR TEMPERATURES IN FORESTS AND OPEN FIELDS. 53 



Very much tlie same is true of tlie muiiiua temperatures. They are 

 always cut off in the annual mean, but by a varyiog amount. The 

 largest reduction of the minima is for Sonnenberg {2°M) ; the smallest 

 is for Melkerei (0o.74), except for the young forest of Liutzel station, 

 where it is only 0^A3. The average amount is lo.33. 



The length of the lines opposite the names of the stations in Fig. 

 9 indicates the reduction of the range in temperature in the woods as 

 compared with the outside. This is a reduction of range, because the 

 forest lowers the highest temperatures of the day and raises the lowest. 

 This reduction varies like the preceding, of which it is the sum for each 

 station. For St. Johann it is 00.25; for Sonnenberg 5^^.92, while it is 

 only 10.80 for Hadersleben and Qo.TS for Lintzel. This is a measure 

 of the degree by which the air temperature is moderated in the woods 

 in the average. The absolute moderation is often greater, as the woods 

 become more efficient in reducing greater extremes, espe(;ially in low- 

 ering the highest temperatures. This is seen by considering the abso- 

 lute range for the year— that is, the number of degrees between the 

 highest temperature for the year and the lowest. The mean of the 

 absolute annual ranges at all the German stations is for the open fields 

 920.90, for the woods 8I0.8G, which gives a reduction of llo.04. The 

 mean range for all stations is 40.IS, or but a little more than a third of 

 this. The value of W—0 for the mean annual temperatures is one- 

 half of the sum of the value of W—0 for the maxima and minima. 

 The reduction of the minima is always less (except for Lintzel, young 

 woods) than the reduction of the maxima, and the combined effect is 

 necessarily a cooling one. On Fig. 9 the position of the mean tem- 

 perature compared with the zero line is the point in the middle of the 

 line i-epresenting the range of W — for each stati<m. This is marked 

 by a short cross line. It will be observed that in every case, except 

 the one mentioned, this mark falls below the zero line, or on the cool- 

 ing side. 



The anumnt of reduction of the mean temperature varies with the 

 reduction of the extremes, and is very different for different stations. 

 For St. Johann it is I0.7O, for Melkerei it is I0.72, but for Knrwien it 

 is only 00.17, while for Lintzel the mean tem])eratnre is 0o.04 higher 

 in the woods than out. The average reduction of mean annual tem- 

 perature for all the Gernmn statitms is 0o.76. 



It appears, therefore, that the forest moderates (by reducing the ex- 

 tremes) find cools (by reducing the maxima more than the minima) the 

 temperature of the air tcithin it. The moderating influence is decidedly 

 greater than the cooling effect. 



MONTHLY RANGE. 



On taking up the consideration of the mean monthly values of W— 

 a very curious series of results appears. Fig. 1() illustrates the influ- 

 ence of the forest on the temperature of its interior air at Friedrichs- 



