The Thoreau-Reynolds Ridge, a Lost and Found Phenomenon

Abstract

planes perpendicular, and at various intermediate angles, to the original planes. Exactly the same results were obtained from these thin sections.The primary purpose of a gypsum plate in optical mineralogy is not merely to increase the birefringence (the quarter-wave mica plate is more commonly used for that) but to indicate elongation. The apatite minerals are optically negative. Prismatic crystals are length-fast, tabular crystals are lengthslow (5). The "blue rim" produced on the articulation surfaces of domestic animal bones when the section is placed so that the edge of the articulation surface is perpendicular to the slow ray of the gymsum plate suggests an alignment of tabular crystals oriented with the basal planes parallel to the surface of bone-to-bone contact. The strong enhancement of (002) reflections from the articulation surfaces corroborates the optical evidence.We hypothesize that the alignment noted is a reaction to stress in the weight-bearing bones of domestic animals which, through poor nutrition or lack of exercise or both, possess insufficient bone matter when compared with the healthier wild animals. McConnell's figure 2 seems to support this hypothesis-the lack of large-scale orientation effects reflects the lack of stress in a fetal tooth. It might be worthwhile to compare the teeth of individuals of different cultural environments with our techniques, although since we have concentrated on the effects produced in the weight-bearing bones, and especially in the articulation surfaces of such bones, we do not know whether dental enamel would reflect similar stresses.ISABELLA DREW

Flow beneath a stagnant film on water: the Reynolds ridge

“…Other published observations of the Reynolds ridge, a surprising number of which appear to have been independent, discoveries, include those by Satterly (1919), Thompson (1919), Burdon (1926), Edser (1926), Satterly & Turnbull (19291, Woog (1931), Schmidt (1936), Stansfield (1936), Hall (1936), Burdon (1949), Bell (1954), Satterly (1956), Merson & Quinn (1965), Sellin (1968), Mockros & Krone (1968) and McCutchen (1970). It is interesting to note that one of these accounts (Edser 1926) was in a textbook of physics.…”

“…However, Reynolds did describe both of the alternative forms of the ridgethe other being seen when a thin surface-active oil layer spreads unhindered on a clean water surfaceand he demonstrated their equivalence. Reynolds' interest in the phenomenon has resulted in its being named after him (McDowell & McCutchen 1971). Rayleigh (1890) also demonstrated the spreading-oil version of the ridge.…”

Dynamics of spontaneous spreading with evaporation on a deep fluid layer

“…Inviscid pressure variations of order U 2 deflect the surface of the uncontaminated water a height, h, determined by the balance U 2 ϳghϳ␥‫ץ‬ 2 h/‫ץ‬x 2 , where the last term represents the Laplace pressure caused by surface curvature in the streamwise direction. 26 It has been argued in the literature 22,23 that this ridge should also form in front of a surface active film rapidly advancing over a quiescent water surface since an observer moving with the leading edge observes the identical flow conditions just described for the stationary monolayer. Studies in which the Reynolds ridge has been carefully measured, 24,25 however, have used oncoming streams of constant velocity whereas the nonvolatile spreading films we have studied experience a constantly diminishing speed, dL/dtϳt Ϫ1/4 , due to the diminished Marangoni stresses created during spreading.…”

“…Although the study of this elevated rim is beyond the scope of this paper and should be studied using optical techniques better suited to measurements of the surface shape, we have reviewed the literature to make contact with previous work reporting advancing rims in free surface flows. Many studies have investigated the shape of the so-called Thoreau-Reynolds ridge, [21][22][23][24][25] whose existence was fully explained by Harper and Dixon in 1974. 26 As described by Scott and others, 24 whenever surface active films accumulate near a surface barrier, they immobilize the surface and resist compression and dilation, forming a flexible surface film.…”

The dynamics of strong turbulence at free surfaces. Part 1. Description

“…There is a further type of separation that occurs on free surfaces and is entirely asymmetrical: at its weakest it is known as a Reynolds ridge (Reynolds 1881;see also McCutchen 1970;McDowell &McCutchen 1971 andScott 1982). Here the surface flow is slowed down, perhaps by gradients of surface-active agents, but only a very thin layer of fluid is at rest.…”