SCIENTIFIC NEWS. 
139 
this facility is much less, and the transition produces more 
noise $ and, when an elevation is about the -g-V of an inch, with 
positive electricity, the point throws out sudden explosive 
brushes, and if an uninsulated ball be presented, it emits long 
zig-zag sparks. The blunter the point, the less it need be de- 
pressed to produce this change in its property, and some varia- 
tions may perhaps follow from variations of intensity. With 
negative electricity the point does not lose its property of 
causing a silent transmission of electricity, till it is very much 
more depressed than in the experiments with positive elec- 
tricity. As a point is in effect a surface so small that one ma- 
chine can cause the electric matter to pass off in a continual 
flux, it is evident that with a great intensity a ball may even be 
considered as a point. 
These are the leading facts respecting points, and they do no 
appear capable of being explained by 2 ny simple statement. To 
me they seem to depend on a fact which is the reverse of the 
electric charge ; but I must reserve this to a future letter, 
and am, 
SIR, 
Your obliged Header, 
R, B. 
SCIENTIFIC NEWS. 
Geological Scciety . 
May 7th, ISIS, 
The President in the Chair. 
Matthew Cully, Esq. of Askeld, Northumberland, 
Thos. Brandram, Esq. of Lee, Kent, 
Were severally elected members of the society. 
The reading of Dr. Mac Culloch’s paper on the Geology of 
certain parts of Scotland, was begun. 
The 
