88 BULLETIN 1233, U. S. DEPAKTMEXT OF AGK1CULTUKE. 



All other stations in the Pikes Peak locality should he subject to 

 less error than the control station, both because nearly all are better 

 protected from direct insolation and radiation, and because the ob- 

 servations have been taken at later hours, "when, ordinarily, the 

 minimum temperature in the iron pipe will have been passed. Both 

 the time and the amount of insolation, however, are probably 

 important in determining the amount of the depression at the 

 observation hour. 



One of the Wagon Wheel Gap stations (WA-1), which has a tele- 

 thermoscope for its 1-foot temperatures, should have no error in the 

 9 a. m. readings, but these may be lower than the mean temperatures. 

 The corresponding south-slope station (A-2), although its ther- 

 mometer has always been hi a wooden tube, is subject to full radia- 

 tion and insolation all the year, but this is not received until late in 

 the day, which probably accounts for the low 1-foot temperatures 

 at 9 a. m. However, in illustration of the variability of this cor- 

 rection with season and time of insolation, it should "be mentioned 

 that at midsummer the 9 a. m. temperatures were found to be about 

 0.9° F. above the daily means, while in the winter they must be several 

 degrees below the means. The data for the high spruce stations 

 should be fairly close to true mean temperatures, because their read- 

 ings have been taken about midday. As the Foxpark and Monu- 

 ment stations have been regularly visited at 8 a. m. or earlier, practi- 

 cally minimum temperatures in the iron pipes may be expected, 

 except that the Monument station, like Station F-4, may receive 

 insolation very early. The sandhills station (H-2) has had only a 

 wooden tube at its 1-foot depth, and is on a northerly slope, both of 

 which factors would tend toward low corrections. 



Seasonal soil temperatures at the control station. — In Tables 25 and 

 26 are presented the results of soil-temperature observations at the 

 control station, by 10-day periods up to 1918, for the 1, 2, and 4 foot 

 depths. Although considerable data have been added at this and 

 other stations since 1918, it is not felt to be necessary to extend the 

 averages; moreover, the use of such data would further complicate 

 the problem of accounting for the 1-foot depressions as described 

 above, since at a number of the stations wooden tubes have been 

 substituted for iron pipes in this later period. 



The following points are noteworthy: 



(I) The mean soil temperature for 1 foot is 3.1° higher than the 

 mean air temperature for this station, and 6° higher it* the correction 

 indicated by Table 24 is u>v(\. For 2 feet it is 5.4° higher and for 4 

 feel i: i- .",.7 higher, only corresponding periods being compared. 



In ! he six years that h;i\e practically complete records, the 

 l-foot animal mean temperature snows an average variation from 

 the normal of i.(»7°. The first two years of observation were doubt- 

 warmer than any since (hat time, although L914 had a very warm 

 growing season, and may have been on the whole as warm as 1911. 



The greatest variation between corresponding decades occurs 

 about the 1st of June, when it amounts to an average for nine years 

 of •'!. 16 . This i^ on account of the effect Iveness of insolation at this 

 time and because of the fact that in some years the soil may be very 

 dry by .lime I : but in other years snows may he occurring at this time. 



i variation in corresponding decades i^ found at the 

 end of the growing season, the first decade of September showing an 



