IDOL] 



PUBLIC DOCUMENT— No. 83. 



25 



Tables X. and XI. show experiiiicnts arranged similar to 

 the two preceding tables, except that atmospheric electricity 

 is substituted for one of the direct currents. The atmos- 

 pheric experiuKMits were conducted with some modification 

 from those })rcviously described with radishes. The prin- 

 cipal diiference, however, consisted in the pole being 47 

 feet from the ground, instead of 35 feet, and the number of 

 copper [)oints was 124, instead of 24. (See Fig. 2, No. 3.) 

 In the latter case we also used a 2<S-inch metal bicycle Avheel 

 to su})port the points at the to}) of the pole ; in the former 

 ari-angcmcnt an inverted umbrella frame was used. In No. 

 2JI we endeavored to maintain a current of .2 milliamperes ; 

 Nos. 31 and 33 gave the usual current, but no attempt was 

 made to obtain averages in the latter. A sensitive galva- 

 nometer usually showed a deflection of the needle when in 

 circuit with the atmospheric electrodes ; and when the wire 

 from the pole was attached to a Thomson self-recording 

 electrometer it was usually sufl5cient to deflect the needle 

 and to charge slightly a glass case of 30 cubic feet capacity. 

 Only occasional observations were made of the strength of 

 the current in cxi)eriments shown in Table XI. 



SuMMAKv. — Showing the BcsuUiy wilh Lelluce (^Lactuat saliva L.) <jiven 

 in Tables VIIT.-XI. 



Treatment. 



Number 



of 

 Plants. 



Average 

 Current, 



in 



Milliani 



peres. 



Total 

 Per Cent, 

 gained. 



Direct current (weak) ; copper plate electrodes; Nos. 23, 

 26, 39, 32, 



Direct current (stronger); copper plate electrodes; Nos. 

 24,27 



Copper and zinc iilate electrodes, connected; Nos. 2.i, 

 28,31,33 



Atmospheric electricity; copper plate electrodes; Nos. 

 30,34, . . . ■ 



0.184 

 0.367 

 0.214 



22.78 

 40.76 

 36.48 

 39.22 



Average per cent, of weight gained, in grams, . 



34.81 



The average percentage of gain shown by lettuce is 

 slightly higher than that given by radishes, although the 

 acceleration is not so great as that shown in the growth of 

 radish tops over roots. There are, however, no instances in 



