Few years later, Stern [8] published another article devoted to the same problem. He
suggested that interaction between the “salt fingers” actually results in hydrodynamic
instability.
3. Experimental observations of the “salt fingers”
The double-diffusive phenomenon has been thoughtfully investigated in numerous
experiments beginning with very simple ones, in which “salt fingers” were explored
in a qualitative way, and ending with very sophisticated experiments, in which “salt
fingers” were examined quantitatively.
Various Gow visualization methods are applied in the investigation of the doublediffusive
systems: shadow graph photography, streak photography may be exploited to
make exploratory studies of the motions which can arise as a consequence of opposing
vertical gradients [2– 4]. Besides that, the elegant optical methods, which provide a
means for the “salt finger” morphology exploration on the basis of density as well as
refraction index distribution in the double-diffusive system, were employed by Shirtclife
[5,9 –11].
Today, it is possible to use charged coupled devices (CCD camera) to track, record
and investigate the double-diffusive systems, as was done in our experiments. We
carried out a quantitative experiment by means of optical tools in order to determine
the typical characteristics of the “salt fingers” such as the planar form, width, length,
area and rate of growth.
In this section, a short outline of the experimental setup is given (see Fig. 1).
We took a glass beaker of volume 800 ml (1), a funnel (2), a glass tube (3) and