TRANSACTIONS OF THE SECTIONS. 
25 
inrhichzisthedistance of the pointy, a the distance between the nearest points of 
fespheres, and r the radius. ^ 
When both hemispheres are equal, the whole force will vary as ^ 
ijtace between the spheres increases, the points 5 q' recede from the surface and 
wiU finally coincide with the centres of the spheres, which would limit the distance 
I! finch a charge could possibly occur. , , •.1, 
TV author exhibited to the Section tlie striking agreement of the calculation witn 
eftnoent, by means of his electrical balance, consisting of a delicate scale-beam 
fii) duly poised suspended sphere ; the weights requisite to balance the force >e- 
twn this sphere and a second sphere placed beneath it, and charged with a 
‘isutity of electricity, were predicted with great precision. In the couree of 
MsoDie ma^etic experiments were exhibited illustrative of the action of the 
nw between siiniiarly placed and opposite points. 
IV author observed, that every kind of case in ordinary ekctricily could be easily 
Mdsoply investigated upon these principles, and that unless the air between con- 
could become charged, no attractive force would be apparent, and tms woxna 
B(an« limit the distance at which such force could exist r it has been shown by 
^wday that with the same constrainiDg power induction takes place more readily 
OTfiihraore difficulty as the extent of the intervening dialectric particles is dimi- 
or increased. We might have electrical corrents in u space devoid of rosist- 
“**• but without an interposed dialectric medium it is doobtful whether those pnm- 
indicative of attraction between the bodies would exist. 
^/romDr.LAMONT (Correspondinr/ MetnUr of the British Assoeiativn) 
to Col. Sadinf.. ., 
Dear Sir, Municli, May 28 , 1841. 
During the last four months I have employed the magnetographic instruments 
^ 1 mentioued to you in a former letter, and find the indicutions so perfect and 
*^'istrumi;nt8 themselves *0 practical—1 mean not easily deranged and requiring no 
i^'btular luhour nor delicacy in their management — that! take the liberty ot giving 
short account of them in case you should think proper to mention the subject 
meeting of the British Association. ^ 
* me construction of the instruinenta is very simple, a few words will be sutn- 
cient to give an idea of it. A magnetic bar 00 
is guspended by a fine wire cd, the upP^;*^ 
which is fixed to a brass spring od. Above tne 
brass spring there is an exceninc/. On turn¬ 
ing the excentric the spring is pressed down oy 
about one Paris line, and the magnetic bar 
lowered by tlie same quantity. At the ends ot 
the bar there arc two fine points of steel «,» 
going downwards: below the points are 
Slimier, of tin C". C' placd on 
Stone pillar. Tlic cylinders are polished, 
surfaces covered with a very thin 
and lamp-black. Wfacu tW bar xs 
turning the excentric. the points 
faces of the cylinders, and make jf^rk- 
so small that they can scarcely he 
hv the naked cve; but, when properly lUu- 
Sinated ar^ seen with a microscope as round 
glittering points on a i^rfecUy 
their diataoce 7icSraS^ 
can be measured with ^ 
A« Boon as the marks arc made the cylmaers are 
.tned by » certain angle. .0 .ha, the nC 
• occuDv a different place; thus a senes of marks 
'■‘^und the circumfcrenceof the cylinder showing the magnetic variations. 
