VERTICAL TEiMPERATUKE GRADIENTS. 



71 



Fautiat's observations. They are all reversed tlirougliout the season, 

 and tlie snininer gradients are about 4-4". Those over evergreens are 

 greater tlian those above the deciduous trees, or, perhaps more prop- 

 erl3^, the gradients decrease as we ascend above tlie top of the decidu- 

 ous trees. 



The observations under tlie direction of Dr. Lorenz-Liburnau at Hied 

 were taken in the warmer months of 1888. Thej^ have been ])ub- 

 lislied (juite recently (1890), an<l came under the eye of the writer only 

 after the preceding pait had been finished. They were not systemati- 

 cally taken, but only at such times as seemed especially suited for the 

 study of especial features, and hence they throw light on some points 

 which the systematic observations do not sufficiently care for. One of 

 these is the change in temperature above and below the crown of foli- 

 age for the same station and time. Dr. Liburuau gives the following 

 mean results from many individual observations. The plus sign indi- 

 cates an increase of temperature upward, the minus a decrease. 



Morning hours 



About noon 



A fternoon 



Early night 



Late night and early morning 



Change- 



The station at 3G.1 feet was in the crown, that at 50.8 feet above it. 

 The distances are not great enough to get good values for the vertical 

 gradients, but it is evident that these are very large, and greater 

 above the crown than below. 



These observations were all taken with a clear sky and calm air. 

 Some interesting figures are also given for the differences between 

 field and forest temperatures when the air is still and when it is in mo- 

 tion. 



The following table gives the values of W— under these circum- 

 stances : 



Morning bour.s: 



Calm 



Windy 



Alioiit noon : 



ralm 



Wimly 



Win.ly 



Afternoon : 



("aim 



Wiuilv 



Under trees, 



10. 4 feet. 



(5 m.) 



First and lastnight hours (calm) . 



-1.37 

 1.19 



c J" c 



-2.11 1.17 



-1. 24 . 70 



-2.47 1.37 



-1.62 .90 



-2.02 1.12 



.76 

 .66 



-2.50 1.42 



Tree crown, 



36.1 feet. 



(11 m.) 



°F. °0. 



—1.53 .84 



+ 1.1,7 .04 



— . 54 .30 



+ .02 .01 



—1.13 .63 



- .54 

 -1. 12 



.30 

 .62 



-3.00 1.70 



Above trees, 



50.08 feet. 



(15. 5 m.) 



+2.16 1.20 

 + 2.29 1.27 



+ 2.29 

 + 2.54 

 1^1.30 



+ 1.03 

 —1.28 



1.27 

 1.41 



.57 

 .71 



-3.19 1.77 



