( m) 
glass scale 1.5 meters long, and subdivided into half millimeters is 
used; it is placed at a distance of 4.325 m. and is illuminated by 
spherical mirror strips 1 ). The tension of the spring is regulated by 
the rod k (fig. 3), which passes through a stuffing box D t in the 
cap D. Vertical motion is communicated to k by turning the nut 
D 4 and at the same time preventing the motion of D s . The tension 
is read through the opening f tl from the pointer l on the scale 5 S0 . 
Before mounting the apparatus, that division of the scale 5 20 is 
determined which corresponds with the tension that is to be used, 
by suspending known weights from the stretching wire. 
The apparatus is, like a stretched string,' very liable to start vi¬ 
brating under the influence of small impulses. This tendency is 
counteracted by immersing the vanes of a vane-damper b s (fig. 6 
and fig. 3) in oil contained in a circular vessel divided into different 
chambers by the partitions b SA . These partitions are attached to a 
cylinder which turns with slight friction in the adjusting tube and 
is therefore carried round by the vanes b so whenever the holder 
must experience a somewhat greater torsion (§4) 5 ). The vanes must 
be wholly immersed in the oil so as to ensure that capillary reactions 
do not bring forces into play (see f4), whose torsional effect could 
not be neglected. In strong fields the torsion oscillations are damped 
extremely well by the Foucault currents. 
The whole holder and spring hang in the adjusting tube f the 
upper end of winch is screwed to the cap D, this cap also carries 
the rod k, and is itself supported by the glass tube C. The adjusting 
tube, consisting of the portions /„/„/„/„ i 3 three times diminished 
m cross-secnon The lowest portion/, is narrow and surrounds the 
od 6 of the holder as closely as possible. Against the bottom /. 
ag. 5) rests the cone c, which is soldered to the wire d and serves 
to keep it taught A slit in the bottom allows the conical portion to 
be placed m position (fig. 5). When the apparatus is put^ogether 
tobe/TlS ^ Vessel * «** thf thin 
tube J IS centred the narrow portion of the vacuum tube The 
Sir.,it “»*• *• - - 
* **«- 
tube C of the cover: the screw. 71 "? 8 C< T nted to the S las8 
cover; the screws D, are tightened, and the junction 
*) H.Kamerlimgh Onwes, Comm. fr. the nh™ r qK t m 
t. . . , me P n y s - Lab. Leiden, n°. 25 flgom 
to prevent the accumulation Sub * tances ’ and als0 
to be completely evacuated after it is put together. ^ *** ** apparatuS haS 
