210 The Electrical Method of Soil Moisture Deterimnation 



lines of equal resistance as shown. These results are quite in accordance 

 with the observations of Gardner (I.e.), who in attempting to standardise 

 a pair of electrodes on an experimental plot found, by actually drying 

 samples, that the moisture content at any depth might vary over a 

 small area by as much as 7| per cent. Although moisture contents were 

 not determined in the present case it will be seen from the resistance- 

 moisture observations given later in this paper (Table VII) that such 

 variations are sufficient to accoimt for the different resistances observed, 

 although it should be remembered that other factors may also be 

 operative, such as variations in the soluble salt content — especially of 

 nitrates — from point to point in the plot. 



Scik of feet £_ 



Fig. 1. Local variations of resistance on plot at 7" depth. 



The Effect, of Distance apart of the Electrodes. Gardner (I.e.) made 

 numerous experiments on this matter by burj'ing two large electrodes 

 15' apart, and a series of smaller ones at distances from J" to 18" apart, 

 15' from each of the larger ones. He then took the resistance between 

 the large pair and between the smaller ones, singly, and each of the 

 larger ones. He adds " From these measurements it was a simple matter 

 to calculate the resistance due to each of the individual electrodes at 



