tributing wires in the ground, which wires are sub- 

 ject to corrosion. 



The use of earth-batteries seems to be a more 

 reliable method of furnishing electricity to the soil. 

 For their successful use the soil should be kept 

 fairly moist, especially around the metallic plates. 

 The use of weak acids in the vicinity of the zinc 

 plates may be of advantage if of any disadvant- 

 age, it would be that they consumed the zinc too 

 rapidly, thus increasing the expense, possibly with- 

 out a corresponding increase in the good done to 

 the crop. The plates should be of ample size, and 

 their distance apart should be regulated to suit the 

 crops planted between them; the greater the dis- 

 tance the larger the resistance to the current and 

 the less its strength. When a current of but little 

 strength is wanted by soils or plants sensitive to it, 

 rows of zinc plates should be connected with rows 

 of copper plates at considerable distances from 

 each other. If stronger currents are needed, the 

 distance should be diminished. A sensitive gal- 

 vanometer inserted in the wire above the ground 

 will be of assistance in finding out the strength of 

 current best suited to the circumstances of soil and 

 crop; it will surely tell us whether or not a current 

 is flowing through the soil: this will point out the 

 cause of occasional failures in this form of experi- 

 mentation. The action of the battery will slowly 

 destroy the zinc, while the copper will last almost 

 indefinitely; so it will be best to raise the zinc 

 plates from the soil when no crop is being grown, 

 or, at least, to disconnect the wires which join the 



