Observations on fluid flows indicate quite clearly that it may be feasible to distinguish between various classes of fluid motions with reasonably well‐defined properties.
Before we try to investigate the feasibility of distinguishing waves from turbulence, it is important to notice that these two types of fluid motion are not the only ones. If all realizable flow patterns are assumed to be solutions to the same set of equations, then in principle they all possess the same degrees of freedom or possible modes of motion. The spatial and temporal boundary conditions appropriate for a given flow field determine which modes can and will be excited.
Electrical conductivity of molybdenite (MoS 2 ) as a function of voltage and temperature.-Measurements of the currents through narrow flat strips cut perpendicular to the crystallographic c-axis gave results for the range from 0° to about 200° C, in agreement with the equation: i -KV h e~kl T , where, for the mineral in the ordinary state, k is about 3,000 and b generally about 1.6. When the voltage is increased to a critical value, breakdown occurs, due to the electric heating. An expression is derived for the breakdown temperature, which is shown to increase as k diminishes. Above 200 0 irregularities appear; and after heating to 400 0 and higher or after current heating beyond the breakdown point, the conductivity at ordinary temperatures is usually permanently improved, and k is decreased. In fact, by the use of proper current cycles, a strip may be transformed by stages from a very poor conductor (resistance several megohms) into a reasonably good conductor (resistance only a few ohms), obeying Ohm's law (b = 1). At the same time, k diminishes and the breakdown temperature rises until the break disappears at the limiting value of k predicted by the equation; also the photoelectric sensitivity and dielectric polarization disappear. A high potential discharge likewise increases the conductivity. This remarkable permanent change of conducting state may indicate a corresponding change of structure from an a to a /3 form, as suggested for selenium. If the constant k is interpreted as being equal to
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