30 
BULLETIN 1059, U. S. DEPARTMENT OF AGRICULTURE. 
changes are in one direction, still there is no basis for assuming that 
for whole years there can be any essential difference. Therefore, if, 
for example, the mean annual temperature at 1 foot, as shown by 
8 a. m. observations, is 49°. and the corresponding temperature at 
4 feet is 50°, there is every reason to believe that the 8 a. m. readings 
at 1 foot give values, on the average, 1° below the corresponding 
daily means. When the oscillations are greatest at midsummer, this 
correction would be too small, and in winter it would be too great; 
but its use should, at least, bring us nearer to the true mean tem- 
perature for any given period. 
Table 1 indicates the correction factors thus obtained for a num- 
ber of stations and sites, with sufficient description of each to show 
why the morning temperature is much or little below the mean for 
the day. Practically all of these records were obtained from ther- 
mometers in iron pipes, which, by conduction, tend to create a 
greater daily range of temperatures in their vicinity than occurs in 
the soil naturally. From these data it will be seen that a small 
variation from the mean is likely to be secured if (1) the aspect is 
easterly so that the site receives early insolation, or ( w 2) if the 
observation hour is relatively late, or (3) if the natural daily range 
is small, as is usually the case with heavy cover and to some extent 
on slopes which do not receive vertical rays. Finally, insolation late 
in the day, though probably causing a large daily range, may bring 
a morning observation relatively high on the descending curve. 
These data will be principally valuable in indicating that every site 
must be studied independently. 
Table 1. — Probable error in mean 1-foot soU temperatures obtained through 
single daily observations. 
[Determined by comparing annual means for 1 foot and 4 feet.] 
Site. 
Station. 
F-l 
F-2 
F-3 
F-4 
F-5 
F-6 
F-7-8. . . 
F-9 
F-ll.... 
F-12.... 
F-14.... 
F-15.... 
F-16.... 
M-l 
W-Al... 
W-A2. . . 
W-F.... 
Average 
ie-.ression 
of 1-foot 
tempera- 
ture. 
Moderat e southerly slope open 
Southwesterly slope, some trees 
Northeast slope, steep, heavy cover. 
East slope, some cover 
Canyon bottom, heavy cover 
Northwest slope 
North slope, no cover 
North slope, full cover 
Flat, little cover 
Do 
North slope, one-1 bird cover 
Dp. 
North slop 
Gentle easl 
North slop 
South slop 
North slop 
high altitude, no cover. 
'ly slope, little cover 
steep, cover 
steep, some cover 
heavy cover 
2. 92 j 8 a. m., strong radiation. 
1. 01 Insolation late in day. 
0. 71 ; Insolation early, range small. 
0.34 | Insolation early. 
1. 40 Insolation late, if any. 
1. 17 Do. 
1. 10 9 a. m., some insolation early. 
0.94 I 9 a. m., little insolation. 
1. 19 7-8 a. m., heavv snow blanket. 
0. 78 ! 8-9 a. m., insolated all day. 
1.11 9 a. m., little insolation. 
0. 97 Do. 
1.38 10-12 a. m., radiation intense. 
0.64 s a. m., early insolation. 
1 0. 38 I 9 a. m., small daily range. 
3. 16 Great daily range.' 
0.34 11-12 a.m. 
1 This station equipped with telethermoscope, so that depression is due solely to normal depression of 
soil temperature at 9 a. in. 
