230 NOTICES OF THE MEETINGS [Jan. 21, 
weighed one grain. It was attached as usual to a torsion head 
and index. The horizontal beam was a small glass tube terminated 
at the object end by a glass hook. The objects to be submitted 
to the magnetic force were either cylinders of glass with a fila- 
ment drawn out from each, so as to make a long stiff hook for 
suspension from the beam; or cylindrical bulbs of glass, of like 
shape, but larger size, formed out of glass tube; or other matters. 
The fine tubular extremities of the bulbs being opened the way 
through was free from end to end ; the bulbs could then be filled with 
any fluid or gas, and be re-submitted many times in succession 
to the magnetic force. The source of power employed was at first 
a large electro-magnet; but afterwards, in order to be certain 
of a constant power, and for the advantage of allowing any 
length of time for the observations, the great magnet, con- 
structed by M. Logeman upon the principles developed by Dr. Elias, 
(and which, weighing above 100 Ibs. could support 430 Ibs. ac- 
cording to the report of the Great Exhibition Jury), was purchased 
by the Royal Institution and used in the enquiries. The magnet was 
so arranged that the axis of power was five inches below the 
level of the glass beam, the interval being traversed by the sus- 
pension filament or hook, spoken of above. The form and posi- 
tion of the terminations of soft iron are shewn in plan by the 
diagram upon a scale of 545, and also the place of the object. All 
this part is enclosed in the box which belongs to and carries the 
torsion balance, which box is governed by six screws fixed upon 
the magnet table; and as both the box and the table have lines 
and scales marked upon them, it is easy to adjust the former on 
the latter so that the beam shall be over and parallel to the line 
a,e with the point of suspension over ¢; or, by moving the whole 
box parallel to itself towards m, to give the point of suspension 
any other distance from the angle c. As already said, the objects 
were constructed with a suspension filament of such length as to 
make them coincide in height with the angle in the magnetic field. 
When suspended on the beam they were counterpoised by a ring 
or rings of lead on the further arm of the beam. These when 
required were moved along the beam until the latter was horizontal ; 
and that state was ascertained by a double arm support, which 
sustained the beam when out of use, brought it into a steady state 
when moving, and delivered it into a condition of freedom when 
required. The motion of the box to the right or left, so as to place 
the object in the middle of the magnetic angle, was given by two 
