TEMPERATURE OF THE SOIL. 425 



to development which the eggs there endure — has uo doubt much to do 

 with the degeneracy of the young k)custs that hatch in the Temporary 

 region. Having already arrived, by experiment (Chapter XIII), at an 

 approximate knowledge of the influence of moisture, and of alternate 

 freezing and thawing on the eggs, we desire in the present connection 

 to ascertain, as nearly as present data permit, the mean temperature or 

 thermal constant at which the eggs will hatch. Experience with this, 

 as with other insects, indicates that there will be constitutional peculi- 

 arities belonging to different individuals which will cause irregularity 

 in development even under the same conditions j but we must recognize 

 exceptions to all conclusions, and desire to ascertain as far as possible 

 the rule. 



The following study, which, though necessarily incomplete, affords the 

 first approximation toward the exact determination of the effects of 

 temperature on the time of hatching of the eggs, has been made for us 

 by Prof. Cleveland Abbe, of Washington. 



THE TEMPERATURE OF THE SOIL. 



On this fundamental question our positive information is meager and 

 unsatisfactory. We need for our Western States observations of daily 

 maximum and minimutn temperatures, or better, four observations a 

 day, at regular hours, of the temperature of the soil at depths of 0, 1, 

 and 2 inches, within such soils and exposures as are selected by the 

 locusts for their eggs. But we are not aware that any such observa- 

 tions have as yet been made anywhere in the United States, and shall 

 therefore be obliged to depend upon some general conclusions drawn 

 from European observations of soil temperature. On this account, and 

 until such observations are instituted in our own Western regions, our 

 investigations will be liable to a considerable range of uncertainty, and 

 we can only indicate general results instead of illustrating our method 

 by definite special cases. 



It is to be earnestly recommended that in future careful observations 

 on the temperature and moisture of the soil be made in connection with 

 the usual record of temperature and moisture of the air, the rain-fall 

 and wind, and cloudiness of the sky. Amateur meteorological observers 

 frequently spend money and time upon barometrical observations that 

 would be more profitably spent upon rain-fall, moisture, and tempera- 

 ture. 



We have prepared unpublished tables, which suffice to illustrate the 

 very various temperatures of the soil under similar atmospheric tempera- 

 tures, depending upon the nature of the soil, exposure, time of day and 

 year, cloudiness, rain-fall, wind, &c. In order to aid in forming an ap- 

 proximate judgment of the temperature to which eggs must have been 

 exposed, it will be necessary to remember that during a few hours on 

 sunny days the temperature within one inch of the surface of the ground 

 is decidedly higher than would be inferred from the observations at 



