1665 
a projecting edge, which fits the cylinder accurately and is connected 
to it air-tight by means of a rubber band; moreover it is forced 
down on the cylinder by means of screws. At the top the tube B, 
is somewhat narrowed down and connected air-tight with the knob 
K by the aid of a thin-walled rubber tube of a few centimetres 
length *). 
The small disk S hangs a few mms. above a ring R,; this ring 
is suspended from three rods, which are screwed into the lid of the 
cap: by screwing the slide downwards it is possible to make S rest 
on A, by which means the tension may be taken off the suspension- 
wire, whereas by moving the slide upwards the oscillating system 
may be again released. 
The plate P is provided with two small hooks to which the 
tube B, may be hooked by means of a band with eyelets. 
If the slide is then moved up, the oscillating system can be lifted 
out of the cap to beyond S; by supporting the ring R, by means 
of a small plate placed underneath, the wire can then be screwed 
out and the cylinder C may be replaced by a different one; or else 
the small rods which carry R, may be unscrewed and the tube B, 
with the lid attached lifted higher, so that the small tube B, may 
be taken out. In this case the sphere B must be first detached ; 
this is done, while the cap is still closed and the disk S still leans 
on f,: the lower half of the spherical vessel is first removed and 
the upper hemisphere shifted up, by which means the sphere B 
becomes completely accessible and may be screwed from the steel 
pin. In mounting the apparatus the same operations are performed 
in the opposite order. 
The levelling of the apparatus is performed by means of the 
levelling screws by which the cap is supported. After the apparatus 
had been mounted, but before the oscillating system was introduced, 
a plumb-line was attached to the knob A, which passed through 
the small hole in the bottom of the lower hemisphere; by adjusting 
the screws it was possible to make the wire, while coinciding exactly 
with the axis of the tube B, (for this purpose the tube was closed 
at the top by a small cap with small hole at the centre), also pass 
freely through the lower opening. When this was attained, thin 
metal wires were soldered in front of the windows in the copper 
1) This air-tight connection did not prevent the knob from being turned through 
a moderate angle, or from being shifted sideways, or the slide from being moved 
up and down, at least over a small distance. In order to prevent the rubber tube 
from collapsing on the apparatus being exhausted a small copper spiral spring 
was pul inside, which did not interfere with the mobility. 
