This paper presents the results of an investigation concerned with measurements of the scale-size of the flow patterns near the so-called Malkus transitions. The flow patterns in a heated fluid layer were photographed at various Rayleigh numbers and these photographs subjected to quantitative analysis using an optical correlation computer. The results showed that the method provides a very sensitive technique for locating the transitions. Transitions reported by other investigators have been confirmed for Rayleigh numbers between 5.0 × 103 and 1.0 × 106, and an additional, previously unobserved, transition has been detected. Heat-transfer measurements were also made. This data demonstrated the limitations, compared to the optical method, of this approach to the detection of transitions.

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