326 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



been exceeded by the ground temperature. This result discourages 

 very early planting. The highest results in Austria-Hungary were 

 obtained from both beet and potato planted on May 1 as against 

 earlier and later dates. When the necessary earth temperature has 

 been reached, then the seeds should be planted. 



The observation of ground temperature ought to be a very important 

 branch of agricultural practice. The temperature at depth s of 1£ to 3 

 inches should be taken daily, and in course of time, when observations 

 and experience have been accumulated, and a classification made of 

 the results for various crops, this will become a more useful and trust- 

 worthy guide to the farmer than the temperature of the air. The aspect 

 or exposure, and also the character of the ground, have of course to be 

 noted in connection with these inquiries. In dry ground temperature 

 increases in some ratio according to the size of the particles up to a 

 certain point, and then decreases. This holds good for the warm sea- 

 son. Oscillations of temperature follow in a similar relation. In moist 

 ground the temperature also increases, up to certain limits, with the 

 size of the earth particles, and the ground in a crumbly condition is 

 warmer than in a powdery or fine state of division. In the cold season 

 the coarser ground is colder and follows changes of temperature more 

 quickly than the less aerated or firmer ground. 



Fine earth can contain more water than coarse earth, but also evapo- 

 rates more, and allows less water to sink through it. Penetrability and 

 evaporation are frequently inversely related to each other. 



Perhaps some results of ground temperature and moisture observa- 

 tions arrived at by the present writer may be here briefly alluded to, 

 though they were on a small scale. When grass or earth is covered 

 over at night by an impermeable material, the moisture from a little 

 below the surface of the earth exhales, but does not escape, and is 

 deposited on the undersurface of the material and on the grass blades. 

 Plants might thus be kept moist, when desirable, by a covering which 

 could be removed at any convenient time in the afternoon and replaced 

 in the evening. Hollows, depressions, and sheltered parts near the 

 hedges are much more bedewed on most nights, excepting the calmest, 

 than fully exposed places, and the intensity of frost and the sun's heat- 

 ing effect a little below the surface is also generally greater — in fact, 

 the daily and annual range of shallow-earth temperature is greater, 

 but all these results depend on the amount of wind at night in the 

 particular district. Dew, though copious under a close covering, is 

 very much below the normal on the earth under loose coverings or 

 under trees. Since moisture combined with frost is often fatal to plants 

 when frost alone is not, it is important to discover the driest and airiest 

 situations for delicate or early vegetables; if frost and fog with calm 

 are probable, but if the climate is subject to frost, fog, and wind, or 

 frost and wind, a more sheltered situation is desirable, according to the 

 nature of the plant, for some suffer more by cutting winds and others 



