670 



has about 8 or 10 per cent of moisture. An electric current from an 

 induction coil is sent across from one plate to the other, and the resist- 

 ance of the soil measured by a Wlieatstone brid,!j;e arran.uemcnt with a 

 telephone instead of a g"alvaii»nncter. The drier the soil the higher will be 

 the resistance. The soil ai»pears to move away fiom the plates, however, 

 and the resistance gradually increases from this cause. The movement 

 of the soil }j;"rains seems to depend npon the barometric pressure, chang- 

 ing temperature, and changing moisture content of the soil. 



This oifers two interesting lines of investigation: (1) To perfect this 

 or some other method for the deternnnation of the moisture in the soil 

 without removing the sample from its natural position in the field, and 

 to investigate this movement of the soil grains to see wlicthcr it is due 

 to the substance of the fiaeign body or whether it is simply due to the 

 form of the snrface, or whether it is independent of tlie i>resence of the 

 foreign snbslance; (li) to study the relation to the nieleorological e(»n- 

 ditions of atmospheric pressure, changing tempeiatnre, iind moisture 

 content of the soil, it would seem that this must have an imporlant 

 bearing on the tleveIoi>meut of roots in the- soil. 



The relation of soils to heat is largely dependent upon the relation of 

 soils to moisture and the amount of moisture contained in the soil. 

 It takes nmre heat to raise the temperature of a pound of water one 

 degree than to laise the temper;ilure of a ]t«uiud of soil the same 

 amount; so that the more moisture there is in a soil the mor«' material 

 there is to be heated, and this added material is harder to heat than 

 the substance of the soil itself. 



Tiie tcmp«'iatuie of the soil will deitend alsu upon tiie amount of 

 evaporation iVom tlie soil. It has been sli(»\\n that IVoni I his cause alone 

 the t^^mpeiatiiie <tf a sandy soil may lie much cooler at nudday than the 

 temperature of a clay soil. If the soils had been dry this woidd have 

 been just the reverse, as the substance of the clay is harder to heat 

 than the substam-e of the sand. 



These matters should be I'onsidered in all soil temperature work, as 

 this ed'ect of nuiisture cm the tenii»erafure of the soil must have an 

 important effect on the development of plants. It shows the necessity 

 also of comparative work. 



It has been shown that the nu'an temiierature of a sandy soil is lower 

 than that of an adjacent clay soil, while the sandy soil is drier than the 

 clay soil. These are conditions of a lower temi)erature and a drier soil, 

 which are used in gn^Mdiouse culture to force the rii)ening of a i)hint; 

 while the higher temperatiu'e and the greater moisture content of the 

 clay soil are conditions used in greenhouse culture to produce a leafy 

 development and to retard the ripening of a plant. 



The field of investigation thus outlined api)ears very important and 

 full of promise of results of great practical value to agriculture. The 

 work as a whole should be systematically arranged and carried out, 

 but there are many dillereut problems which could be taken up and 



