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

and foated and this operation repeated
several times, the rod becomes more
and more repellent of water and when
depressed in the water-Surface by a
fine wire the lines of separation of the
glass and water become almost straight
and the rod acts like one of clean metal
THE experiments on the metals show
that, when their surfaces are freed
of air, they sink, and that, after the
film of air has recondensed on their
surfaces, they float. In other words.
in the first case the metals are wetted
and in the second they are not. 1t is
evident that the dry surface of the
wire between the two opposite de-
pressed surfaces of water could not
exist if the water wetted the wire as
1t would wet a ring made of clean
glass. At the same time, though the
water does not wet the wire as water
vets glass, yet the water is attracted
by the Wire so that it adheres to 1t
with such force that it can take thr
curvature required to withstand fine
inward hydrostatic pressure on the
two depressed water surfaces Another
observation is Of interest here. Or
observing the wire between the de-
pressed sheets of water through a mi
! croscope, one does not see the oppo-
site surfaces of the water gradually
and smoothly slide over the wire and
approach one another as the wire goes
deeper and deeper in the depression
but the terminal edges of the de-
pressed water surfaces leave the wire
to approach one another in a series Of
jumps. These releases of the two edges
OF the water surfaces from the wire
dc not take place uniformly and sim
ultaneously along the whole of these
edges, but take place at many points
lrregularly distributed along the lines
OF demarcation Of the wire and water
The attraction existing between the
wire and the water is shown by lift
ing a floating ring above the general
surface of the water when the wafer
adheres to the ring and may be lifted
several millimeters. If the ring be
lifted quickly, we often obtain a cate
mold Of elevated water-film apparently
centimeter or more in height When
the elevated film breaks, it generally
forms into drops regularly spaced
around the ring
The film of air on the surface of
! the rings must be very thin, probably
a small fraction of the radius of molec.
ular activity. IT, however, the air be
condensed on the metals to the same
degree that oxygen is occluded by plat :
mum black, the air film may have the
density of water, and its attraction
Of the metal itself for water. This
condition, which probably exists rem
ders futile the determination of the
thickness Of the air film by optical
methods.
Prof. Wright, of Yale university,
suggested to me to determine if total
reflection took place from a water sur
face which was in contact with a sur.
face Of metal. 1 made the experiment
III the following manner:
"a cubical vessel, made of plates Of
glass, was about two-thirds filled with
water, and a black cross on q white
ground was seen by total reflection
from the surface of the water. A
floating disc Of aluminium was moved
till it came over the portion of the
water from which the reflection had
taken place. The reflection was de-
stroyed by the presence Of the disc, and
this destruction took place either with
disc whose surface was partly pol
ished, or with disc whose under sur
face had been made of non-reflecting
gray by the action Of caustic soda.
This fact is interesting, but I do not
see how it can give information even
as to the limiting thickness of the film
of air of whose condensation and index
Of refraction we know positively moth
ing. ALFRED M Mayer
Professor Stevens Institute of Tech
nology."