273 
climates upon our crops. These tables must include at least the 
following data: 
1. The mean temperature of the air in the shade. This may be 
deduced most simply from the average of the daily maximum and 
minimum temperatures. 
2. The mean temperature of a thermometer, preferably a black 
bulb, but not in vacuo, exposed to the full sunshine and wind and 
placed amid the foliage of the trees or the blades of the grain that 
is to be studied, so that its temperature may be approximately that 
of the plant. This should also preferably be obtained by using 
maximum and minimum thermometers. 
3. The temperature of the soil at depths of 1 inch and 6 inches, 
corresponding to the depths of the roots of the plants. 
4. The hygrometric condition of the free air, which may be 
expressed either as relative humidity or as dew point or as vapor 
tension. The latter will be most convenient in all our calculations. 
5. The velocity of the wind or its daily movement. 
6. The cloudiness of the sky. This may be obtained from the 
ordinary estimates of cloudiness if these are made very frequently, 
but with more ease and accuracy from some form of sunshine recorder. 
7. The total effective radiation from sun and sky. This may be 
obtained from frequent observations of the Marié-Davy actinometer 
or the so-called Arago-Davy conjugate thermometer, or Violle’s conju- 
gate bulbs, but still better when these are made self-recording, and 
better yet from such forms of apparatus as the photantitupimeter or 
phantupimeter of Marchand, or the radiometer of Bellani, which 
Marié-Davy has improved upon in the form described by him as the 
vaporization lucimeter. (See Annuaire de Montsouris, 1888, p. 207, 
or 1890, p. 61.) The methods of using these instruments are doubt- 
less subject to improvement, but these or some more delicate sub- 
stitutes are absolutely necessary in order to enable us to appreciate 
the work done by solar radiation. In the absence of instruments 
we may use the maximum sunshine as diminished by the estimated 
cloudiness. 
8. The actual evaporation from plants and soils, or in lieu of this 
the evaporation recorded by the Piche or even older forms of evapo- 
rimeters whose records are doubtless closely parallel to those of the 
plants in the soil, but usually largely in excess of these. 
9. The total rainfall as measured by the ordinary rain gauges in 
the experimental field. 
As an illustration of the convenience of such tables I have com- 
piled the following table for Montsouris by pentads in so far as the 
data is given by pentads by Descroix in the Annuaire for 1890. 
Some of the data is obtained by interpolation from monthly values 
2667—05 M——18 
