32 HATCH EXPERIMENT STATION. [Jan. 



consists of a delicate quadrant galvanometer and a self- 

 registering ap})aratus. A full descrii)tion of this instrument 

 ma}' be found in the twenty-eighth annual report of the Mas- 

 sachusetts Agricultural College, for 1(S91. 



We used a large glass case, with a wooden frame, 4 feet 

 3 inches long, 2 feet 9 inches wide, and 2 feet 11 inches 

 high, with a detachable door in the middle of one side, from 

 which every part of the case Avas accessible. The door was 

 made to fit tightly by a band of rubber around the edge, and 

 was securely held in place by levers. When closed, the 

 case was practically air tight, and was insulated from the 

 stand by glass and rubber insulation. In one corner of 

 the case a small Avater-dripping api)aratus was placed. This 

 apparatus consisted of a light eight-quart copper tank, with 

 a projecting pipe which ended in a fine orifice ; the Avater 

 passing through the pipe immediately broke into drops, and 

 Avas caught in a glass dish beloAV. An insulated Avire con- 

 nected the case Avith the electrometer near by. A short 

 time after the dripping started the tank Avas found to be 

 electrified, presumably to the same potential as the air at 

 the i)oint of the projecting tube. The potential Avas im- 

 parted through the conductors to the electrometer, and a 

 deflection of the needle ensued. 



In the case Avas also placed a self-recording hygrometer 

 (Richard Bros., Paris) and a self-registering thermometer. 

 The case Avas charged in some instances through a Avire at 

 one end leading from a IToltz influence machine. Inune- 

 diatel}' after charging, the Avire Avas withdrawn from the 

 case, and the hole through Avhich it Avas inserted Avas tightly 

 plugged. At other times the case Avas charged from a Le}^- 

 den jar through the same Avire. This seemed necessary in 

 order to get tJie retjuii-ed small potential. The air in the 

 case Avould hold a })art of its charge for about three hours; 

 at the end of that time Ave could find no trace of auA" elec- 

 trical potential. The growth of the i)lants Avas measured 

 in some instances by a modified Pfeft'er-Baranetzky self- 

 registering auxometer, and in other cases by the use of a 

 horizontal microscope Avitli a micrometi'r scale attachment. 



