30 HATCH EXPERIMENT STATION. [Jan. 



positive potentials, and practically the same relative differ- 

 ences are shown here as in the numerous negative potential 

 readings. 



The collector in the branches of the spruce tree, 12 feet 

 from the ground (Collector III.), from which it was well in- 

 sulated, invariably showed the opposite potential from that 

 obtained in the free air and from the elm tree. It will appear 

 from this that the air surrounding the collector in the spruce 

 tree was charged with the same kind of potential (positive 

 or negative) as that of the earth; and the readings taken 

 from Nos. IV. and V., which were very close to this tree, 

 although four feet higher, gave the same kind of potential as 

 that of Collector III. , or larger spruce tree. In other words, 

 all the potentials in Nos. III., IV. and V. are opposite to that 

 of the air. There were some difficulties experienced in ob- 

 taining readings of the tliree spruce trees, — partly because 

 the readings had to be taken too close to the ground, and 

 partly, perhaps, because we were dealing with the same kind 

 of potential in the air that the earth was charged with ; and 

 that, therefore, when the potential of the air in the branches 

 of the spruce tree and the potential of the earth were the same 

 in degree and kind, differences in potential would not exist, 

 and therefore measurements would be impossible. Evergreen 

 trees, which are supplied with a large number of pointed 

 leaves, may possibly be better adapted to discharge elec- 

 tricity than deciduous trees. It is quite possible that ever- 

 green trees behave quite differently from deciduous trees as 

 regards their relationship to atmospheric electricity. In our 

 opinion, there is a strong probability that all living plants act 

 as conductors, or that they serve to keep the potential of the 

 earth and the air in more or less equilibrium ; and that trees 

 and vegetation in general take part in this, although in all 

 probability all species do not act in the same specific manner. 

 This phase of the subject has not been studied as much as 

 is desirable. We infer from our own observations that some 

 trees show a great tendency towards conducting the electricity 

 from the air to the earth, and that other trees show the 

 same tendency for conducting electricity from the earth to 

 the air ; and that in all probability this exchange of elec- 

 tricit}' from tiie air to the earth, and vice versa, does not take 



