The Saint Paul globe. (St. Paul, Minn.) 1896-1905, 1897-07-25

contaminated on the side of the strip
towards which this is moving, while
the surface of the water on the other
side Of the strip has been swept clean
and may be regarded as clean surface.
The platinum ring is f1oated on this
clean surface and the weight required
to sink the ring is determined. Now
load the ring till it's weight is less than
the weight required to sink it by 10,
20, 30, etc, per cent. If the ring is
now f1oated near one end of the trough
while the strip Of metal is slid along
from the other end of the trough to-
wards the ring, the surface of the water
on the side Of the strip toward the ring
becomes more and more contaminated,
till it's surface tension can no longer
hold up the ring, and this sinks. Know
ing the percentage of the breaking
weight with which the ring is loaded
and the fraction of the length Of the
trough to which the strip has been
moved when the ring sank, we have
the degree of contamination of the wa
ter of the trough before it was alter
ed by the sliding strip.
There is no difficulty in obtaining q
| contamination surface. The surface of
| distilled water is contaminated soon
after it has been poured into the
| trough; and, no doubt, was contamin-
| ated before it was poured from the
8
OF contamination of surface is required,
| It may be obtained by introducing into
| the water the point of a needle which
has been coated with a thin film of
| oil, or, by scraping camphor over the
| surface of the water. very thin film
| OF oil, whose thickness Lord Rayleigh
| has fixed as equal to one and one-half
millionth of millimeter. or 1-4O0 of
| the length of wave of yellow light,
| is sufficient to stop the motions Of
minute, thin scrapingS of camphor. If
the motions of the camphor however,
continue with the degree of contamina-
ton we have given the water we can
stop these motions by increasing the
contamination on sliding the metal
strip along the trough and contracting
the contaminated surface. If the ring
floating on this portion of the liquid is
now loaded till it sinks, we have the
means of knowing the diminution of
| the surface tension required to stop
| the motions of the camphor.
eff the ring is placed near one end
! of the trough and the strip of metal
| is slid from the extreme of the trough
| towards the ring but not near enough
| to it to cause such lowering of surface
! tension that the ring sinks, one will
| observe the ring to move slightly away
! from the moving strip. This is owing
| to the contamination of the surface
surface
| tension lower near the side of the strip
| toward the ring than it is at distance
| from the strip, near to and beyond the
| floating ring. The consequence is that
| the surface film surrounding the ring
and beyond it contracts and carries
! the ring away from the strip. The
| strip now remaining stationary, we
| have lower tension on the con-
taminated or ring side of the strip than
on the other side, where the surface
| Of the water is clean; therefore on
sliding the strip backwards with a
gradually increasing velocity over this
clean surface, or, on removing the strip
from the trough, the clean surface con-
tracts and keeps on contracting till it
has so stretched the contaminated sur
face that it covers uniformly the whole
surface of the trough. The ring, hung
in this surface. which is being stretch
ed, moves with 1t and is seen to go
rapidly towards the other end of the
trough.
eff platinum. gold, or silver wire of
40 millimeter in diameter is formed
into ring, heated to redness and when
cold placed on water, it sinks. If the
ring is wiped dry, and then placed on
the water, it sinks, but if wiped dry
and exposed to the air for from ten
to fifteen minutes, 1t will float. Also,