Mr Foggo on tlte Negative Electricity of Showers' 12# 



ther, its alternations with the positive are in general so rapid, 

 that it is difficult to note them down, and the changes from 

 positive to negative are frequently interrupted by periods in 

 which it becomes null. If an electrometer be attached to a 

 conducting rod, when an electrical shower or hail cloud is ap- 

 proaching, the phenomena are as follows : While the cloud is 

 still at some distance, the air is generally strongly charged 

 with -f E. ; when the foremost portion of the cloud is nearly 

 over the conductor, the electrometer collapses, and then ex- 

 pands with — E. ; this state lasts a short while, when -f E. 

 shows itself, and continues till the cloud has passed over, when 

 — E. makes its appearance, and is again succeeded by the na- 

 tural positive electricity of the atmosphere. 



Mr Howard of London appears to have first distinctly stat- 

 ed, that the electricity at the circumference of a nimbus is 

 negative, while that of the centre is positive. This ex- 

 perienced meteorologist observes, that it would be very inter- 

 esting to ascertain whether the negative electricity is ascend- 

 ing; and the positive descending. About the end of the year 

 1823, I became anxious to make the experiment, conceiving 

 that, if these ideas were found to be correct, they might be 

 useful in explaining certain electrical phenomena, the history 

 of which is at present very obscure. For that purpose, 

 I prepared an apparatus, resembling that of Bennet, and 

 connected with it a gold-leaf electrometer. No favourable 

 opportunity occurred till the month of March 1824. On the 

 12th of that month, we had, at this place, a brisk wind from 

 the N. W., with frequent showers all around. About 3, 

 p. M., large dense clouds passed over the zenith, letting fall 

 heavy showers of hail. The conductor was armed with a 

 smoking match, and erected from a south window. 



During the intervals of the showers, the electricity was 

 always positive, and made the leaves diverge to their full ex- 

 tent. Indeed, the electrical tension of the air was so great, 

 that a detached electrometer was fully charged by the slight- 

 est friction with a piece of dry silk applied to the brass cap, 

 and even rubbing the outside of the glass with soft leather 

 opened the leaves to more than 40°. 



During the showers, or when the clouds were over head, 



