Sir W. Snow Harris’s Researches in Statical Electricity. 93 
applied on the surface at the foot a of the cylinder ap, or to its 
distant face p; at the centre (fig. 9) the force was found to vary 
considerably between the base and altitude of the cylinder itself. 
The following are the numerical results :-— 
At centre c. 
{e) 
Force on surface, 7°. Force at remote face of cylinder, 38°. 
At extremity q. 
Force on surface, 32°. Force at remote face of cylinder, 33°. 
15. Exp.9. Having satisfactorily investigated this fact, I pro- 
ceeded to observe the rate of increase of force at the centre as 
the altitude of the intervening cylinder above the surface was 
increased, and to find the altitude of the point at which it would 
become equal to the force at the extremity, viz. 32 to 33 degrees. 
With this view I employed a series of small cylinders of gilded 
wood, varying from ‘1 to *75 of an inch in altitude, and about 
‘4 of an inch in diameter; also other similar cylinders varying 
from 1 to 6 inches in altitude, so as to obtain, by superposition 
or otherwise, any given height above the surface required. The 
following are some of the resulting forces as compared with the 
altitude, in which it is apparent that the force up to a certain 
limit increases with the square root of the altitude, or is nearly 
in that proportion, after which it ceases to increase, and is for 
further altitudes nearly the same. 
Results of Exp. 9. 
neerenny st merre rege re wereer vee Shh. SV) 'e (EAR TAO DSY AOR 
Height above surface in inches.| *]. | °25.] °5. |°75.} 1. | 1°5| 2. | 2°5.| 3. 
Reactive force in degrees.| 7 | 11 | 15} 20] 22/25 | 28| 81 |32 
On employing a cylinder from 5 to 6 inches high, the force 
from the plane with a given charge was observed to be every- 
where the same. 
16. It appears, therefore, from these results, that the effect of 
the intervening cylinder is to raise up the point of contact, and 
place the tangent or proof-plane p, so far without the influence of 
the electrical stratum upon the surface as to admit of a free in- 
ductive change ; the cause, therefore, of a tangent disc of small 
thickness becoming more highly charged from the extremities 
of an electrified surface than from the centre, may mainly depend 
upon its position in respect of the electrical stratum (12) when 
placed in these two relative points. I have on a former oc- 
casion called attention to this circumstance. If, for example, 
we place a small disc of little thickness in the centre of a charged 
