TREE TOP AND OPEN FIELD TEMPERATURES. 63 



The correction which is used is that given by Mr. Ferrel in his 

 "Recent Advances in Meteorology," and is taken from the colnnm 

 for "the Alps and Germany" in the table on page ISO. In no place 

 does this correction, as applied to the German tree-top observations, 

 surpass O'^.ll F., (O.OO^c) and it is always negative. After making 

 this correction the observations will be treated as if the li(;titious ele- 

 vated stations were real and the values of W — 0' (here primed to dis- 

 tinguish from those at the level of 5 feet) Mill be discussed as were 

 those of W — in the preceding section. 



Fig. 23 rei>resents the mean annual values of W — 0' tbr maxima and 

 for minima; the maxima always negative and below the zero line, the 

 minima always positive and above. The names of stations are placed 

 opposite the lines wliicli belong to them, and for each station is given 

 the elevation in feet above the surface of the ground. As in the pre- 

 ceding section, the length of the line indicates the reduction of range 

 of temperature in the tree top, as compared with that outside at the 

 same height, and the point in the middle of tlieline (marked by a short 

 cross bar) indicates the reduction of mean temperatures. 



This diagram presents the same features as the corresponding one 

 for lower levels, but there is, if anything, more variation tor the indi- 

 vidual stations. Also, the mean temperature is here sometimes higher 

 in the tree tops than over open fields. This is the ca.se in five out of 

 sixteen stations. 



It is noteworthy that tlie reduction af the annual temperature in 

 tree tops does not appreciably depend on the height of the station 

 above the ground. The lowest (Schoo) shows the smallest reduction of 

 temperatures. It should have the largest because nearest the ground. 

 On the other hand, the highest station (Hagenau) stands about mid- 

 way. The next highest (Kurwien) stands somewhat lower in the 

 series, while one of the two next highest (St. Johaun) leads the series. 

 Nor does any feature (reduction of maxima, minima, or mean tempera- 

 ture) show any distinct distribution with reference to the height of the 

 station. 



Taking up the individual tree-top temperature diagrams we find 

 them strongly resend)liug those for the observations at the 5-foot 

 level, but with greater variation between the individual diagrams. 

 That for Friedrichsrode (Fig. 21) is a fairly smooth and representative 

 one, and it greatiy resembles those of the preceding section. The 

 minima are raised, the maxima lowered, the action is a cooling one, 

 and it is most marked in summer. These features are all visible in the 

 temperature diagrams at the 5-foot level. The cooling eft'ect is, how- 

 ever, sometimes distributed thrcjugh the year with some a])proach to 

 evenness. 



The reduction of the minima is often relatively great (Fig. 26, St. 

 Johaun). It is not rare that this is greater than the reduction of the 

 maxima, leaving not a cooling, but a warming action on the part of the 

 woods. 



