89 
usually greater than 7, but whose relative value may by preference 
be determined by referring each pair of conjugate thermometers to 
an adopted standard pair. Ferrel’s formula is especially devised 
for thermometers having spherical bulbs, measures made by it at high 
and low temperatures give results that are comparable with each 
other; for absolute results the numerical coefficients may need some 
modification, but as it stands it gives the values of g approximately 
in calories per minute per square centimeter. 
Omitting for the present the factor / in Ferrel’s formula, which 
must be specially applied for each thermometer, we have the values 
of g in calories as given in the following table (see Ferrel, p. 37), 
which also presents the corresponding values given by the formula of 
Marié-Davy in actinometric degrees. In a critical study of observa- 
tions reduced by these two methods we have to recall that Marié- 
Davy’s actinometric degrees are really fractions of a calorie, or units 
of heat so small that 100 of them are equivalent to the absolute radia- 
tion of the sun received at the outside of an atmosphere whose coeffti- 
cient of transmission is 0.875; whereas Ferrel’s calories have been 
adopted without predicating anything as to the solar radiation or 
atmospheric absorption, concerning which his observations show that 
the solar radiation constant is between 2 and 2.25 calories per minute 
per square centimeter and the atmospheric coefficient of transmission 
to be used with the conjugate bulbs is 0.72. 
Solar radiation deduced from observations with the conjugate thermometers. 
Marie | Ferrel, calories per minute per square centimeter for the respective 
Davy, | bright-bulb temperatures. 
aul actino-| — —= 
* |metric | | 
de- —10° —5° | 0° +5°° |) 10° = -+-15° | +20° | +25° | +30° 
grees 
== es | _ eS Se eee 
OC; 
5.....| 29.4| 0.166} 0.172] 0.179 | 0.186 | 0.194 | 0.201 | 0.209} 0.217 | 0.226 
| | | 
10_---| 58.8 | .339 | .352 .366 | .380 885 |  .410 |. 426 .443 | .460 
1a weee |r 18852 .518 | .538 559 581 . 604 | . 627 . 652 .678 | . 704 
Pe Vercele EE 705 | . 132 761: | 791: . 822 .854 | .887 .922 | .958 
25_---| 147.0 898 | . 933 .969 | 1.007 | 1.047 | 1.087 | 1.131 | 1.175 | 1.220 
30_..-| 176.4] 1.099) 1.142) 1.187 | 1.284] 1.282) 1.332) 1.385] 1.4388 | 1.495 
85_...| 205.8 | 1.309 | 1.360) 1.418 | 1.469] 1.526) 1.585 | 1.647 | 1.712 | 1.778 
40.___| 235.2 | 1.525 | 1.585 | 1.646] 1.711] 1.778 | 1.848 | 1.920] 1.995 | 2.073 
45.___| 264.6 | 1.750 | 1.820] 1.891 | 1.964] 2.042 | 2.121 | 2.204] 2.291 | 2.380 
| 
INTENSITY AND DURATION OF SUNSHINE AT MONTSOURIS. 
In order to have at hand data that will enable one to approximately 
infer some of the relations between the temperature of the air and 
of the soil and of the solar radiation, one may consult the tables for 
the observations at Montsouris, given by Marié-Davy in his Annuaire 
for 1887. 
