354 Observations on Electricity. 
During the month of October last, I made a number of experi- 
ments with a view to ascertain the utility of presenting points 
only upon one side of the plate in the electrical machine. My 
attention was called to this subject by a singular experiment 
shown to me by Mr. Daniel Davis, which for some time appeared 
rather enigmatical. A circular plate of glass was charged by 
movable coatings, and on removing the coatings, it frequently 
happened that both sides of the plate when presented toa charged 
électroscope, exhibited signs of the same species of electricity. 
After numerous repetitions with a very careful examination, it 
appeared that only the central portion of the negative side was 
charged negatively, while a considerable annular space exterior 
to this, was charged positively ; the redundant positive electricity 
having forced or spread itself over the edge of the plate. On 
reversing the experiment and making the redundancy upon the 
negative side, the negative electricity appeared to pervade both 
surfaces as did the positive before. Some of our instrument 
makers have been in the practice of placing the collecting points 
of the prime conductor only upon one side of the electrical 
plate, finding that they answered better in many cases, than a. 
row of points upon both sides, although no satisfactory reason 
has been given for this difference. After witnessing the above 
experiment, it occurred to me that the difference was owing to 
the facility with which electricity distributes itself upon glass, 
especially if it be not entirely clear and dry. Experiment fully 
confirmed my anticipations, and I was surprised to find to what 
extent the plate might be discharged by the application of a con- 
ductor to any part of its charged surface. The prime conductor 
having been removed, the plate was turned several times and the 
silk fies: thrown back leaving both sides of the plate exposed in 
a highly charged state. The hand was then laid upon the plate 
at some distance from the edge and quickly withdrawn. On ex- 
amining the plate not only the parts under and contiguous to the 
hand were discharged, but the whole of that portion directly op- 
posite to the hand on the other side of the plate was found dis- 
charged to the same degree, although the distance over the edge 
of the plate was in some cases fifteen inches. It will be found 
that single or only two points on each side of the plate and near 
its circumference will succeed better than numerous points upon 
one side. 
