126 Contributions to Meteorology, 



though no precipitation took place, the E. was invariably po- 

 sitive, and of such intensity, that I could at any time draw 

 sparks from the conducting-wire, by presenting my finger to 

 it. I likewise ascertained, that, by taking hold of the wire, I 

 could at pleasure intercept the fluid from reaching the instru- 

 ment, so that the charge was, without doubt, received from 

 the atmosphere or cloud. On the other hand, when the edge 

 or circumference of the cloud was nearly over the conductor, 

 the electricity became — , and appeared to be fully as strong 

 as the positive charge. I found, however, that it could not 

 be intercepted as before, by taking hold of the wire, nor by 

 touching it with a pointed steel rod. The fluid was, therefore, 

 not proceeding from the cloud as before, but was given off by 

 the earth to the cloud. By presenting the steel point to the 

 instrument itself, the divergence was so much increased as to 

 endanger the gold-leaf, and sparks were heard to pass rapidly 

 between the point and the electrometer, while sharp pricks 

 were felt when the finger was approached to the brass cap. 



In experiments on atmospherical electricity, I sometimes 

 find it most convenient to employ an electrometer of the con- 

 struction represented in Plate I, Fig. 31. It consists merely 

 of a pith ball suspended by a fine silver-wire from a ring or 

 loop, imbedded in sealing-wax, by which it is attached to the 

 lid of the instrument. The lid is of turned wood, and through 

 it are inserted the two glass tubes A. A. These tubes are 

 about one-third of an inch in diameter, and are coated with 

 sealing-wax on the internal surface. Brass knobs or caps are 

 fixed on the lower ends of the tubes. Into one of the tubes, 

 the end of a chain, proceeding from the conducting rod, is fix- 

 ed so as to insure direct contact with the knob or cap, and a 

 similar chain is placed within the other tube, to establish a 

 communication with the earth and knob. The latter chain is 

 about two yards long, and is covered with oiled silk, except 

 at the ends ; it is secured in its place by a pledget of silk. 



When the conductor is elevated with this instrument at- 

 tached to it, and the end of the covered chain rests on the 

 earth, the pith ball is attracted by the knob connected with 

 the conductor. It then carries the charge it has received 

 to the other knob, and is thus made to vibrate between them 



