32 HATCH EXPERIMENT STATION. [Jan. 



consists of a delicate quadrant galvanometer and a self- 

 registering apparatus. A full description of this instrument 

 may be found in the twenty-eighth annual report of the Mas- 

 sachusetts Agricultural College, for 1891, 



AVe 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 was accessible. The door was 

 made to fit tightly by a band of rub])er 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 water-dripping apparatus was placed. This 

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

 a projecting pipe which ended in a fine oriiice ; the water 

 passing through the pipe immediately broke into drops, and 

 was cauo-ht in a olass dish below. An insulated wire con- 

 nected the case with the electrometer near by. A short 

 time after the dri})ping started the tank was found to be 

 electrified, presumably to the same potential as the air at 

 the point of the projecting tube. The potential was im- 

 parted through the conductors to the electrometer, and a 

 deflection of the needle ensued. 



In the case was also placed a self-recording h3^grometer 

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

 The case was charged in sf)me instances through a wire at 

 one end leading from a Iloltz influence machine. Imme- 

 diately after charging, the Avire was withdrawn from the 

 case, and the hole through which it was inserted was tiuhtlv 

 plugged. At othta* times the case Avas charged from a J^ey- 

 den jar through the same Avire. This seemed necessary in 

 order to get the required small potential. The air in the 

 case Avould hold a part of its charge for about three hours ; 

 at the end of that time Ave coidd find no trace of any elec- 

 trical potential. The groAvth of the plants Avas measured 

 in some instances b}^ a modified Pfefler-Baranetzky self- 

 registei'ing auxometer, and in other cases by the use of a 

 horizontal microscope with a micronu^ter scale attacliment. 



