ALBERT

Description: This paper proposes a theory of collisions between small drops in a turbulent fluid which takes into account collisions between equal drops. The drops considered are much smaller than the small eddies of the turbulence and so the collision rates depend only on the dimensions of the drops, the rate of energy dissipation ε and the kinematic viscosity v. Reasons are given for believing that the collision rate due to the spatial variations of turbulent velocity is shown to be [formula omitted], valid for [formula omitted] between one and two. A numerical integration has been performed using this expression to show how an initially uniform distribution will change because of collisions. An approximate calculation is then made to take account also of collisions which occur between drops of different inertia because of the action of gravity and the turbulent accelerations. The results are applied to the case of small drops in atmospheric clouds to test the importance of turbulence in initiating rainfall. Estimates of ε are made for typical conditions and these are used to calculate the initial rates of collision, the change in mean properties and the rate of production of large drops. It is concluded that the effects of turbulence in clouds of the layer type should be small, but that moderate amounts of turbulence in cumulus clouds could be effective in broadening the drop size distribution in nearly uniform clouds where only the spatial variations of velocity are important. In heterogeneous clouds the collision rates are increased, and the effects due to the inertia of the drop soon become predominant. The effect of turbulence in causing collisions between unequal drops becomes comparable with that of gravity when ε is about 2000 cm2 sec−3. © 1956, Cambridge University Press. All rights reserved.

Description: The Arctic Institute of North America was established in 1945 in two small rooms in McGill University, with a staff consisting of Dr Lincoln Washburn and a secretary, who made up for the lack of equipment and facilities by abundant energy and enthusiasm. Since then the Institute's growth has been considerable, always in the direction of its three main objectives—to form a centre for reference information and study on the North American Arctic, to encourage arctic scientific research in any field, and to disseminate arctic information by means of a journal, other publications, and lectures.

Description: Can words freeze as soon as uttered, and thus become inaudible? Polar research does not confirm it, and even the layman may well suspect that there are serious scientific objections to such a notion, and to its corollary, which is that congealed words should become audible on thawing. Yet this idea, through the ages, has given rise to a series of literary anecdotes and allusions, all of them humorous or satirical in intention. It is interesting to speculate how the idea arose in the first place. Hyperbole, including deliberately facetious hyperbole, is always present in the popular imagination, which tends to seek vivid, graphic, and sometimes wildly improbable comparisons in order to make its point. The heat of hell, and the coldness of charity, are equally undemonstrable from the strictly scientific point of view, while the goodness of gold must be regarded as ethically unverifiable, however effective as alliteration. We must imagine that some early wit once said: “It's so cold in X that when you try to say something, your words freeze and fall to the ground.” As a matter of fact, something very similar was attributed by Plutarch to one Antiphanes. In a chapter of the Moralia entitled “How a man may become aware of his progress in virtue” we find this anecdote:Antiphanes said humorously that in a certain city words congealed with the cold the moment they were spoken, and later, as they thawed out, people heard in the summer what they had said to one another in the winter; it was the same way, he asserted, with what was said by Plato to men still in their youth; not until long afterwards, if ever, did most of them come to perceive the meaning, when they had become old men.

Description: The existence of high rock thresholds beneath the glaciers of Dronning Louise Land is established and examples are described. It is concluded that decrease in the height of the Greenland Ice Cap and the consequent emergence of the rock thresholds is the dominant factor in the final stages of recession of the glaciers of Dronning Louise Land. It is tentatively suggested that this process has more than local significance, and may be an important factor in the recent recession of the glaciers in other parts of east Greenland.

Description: Small spheroidal particles suspended in a sheared viscous liquid are sometimes observed to take up slowly preferred orientations, relative to the motion of the undisturbed liquid, which are independent of the initial conditions of release. These obsevations cannot be accounted for by the solution, obtained by Jeffery (1922), of the linearized Navier-Stokes equations. It is shown in this paper that the effect of the inertia of the liquid is to alter slowly the orbit of the particle in accordance with Jeffery's hypothesis that the particle ultimately moves in such a way that the dissipation of energy is a minimum, but that this effect is orders of magnitude too small to account for any of the experimental observations. It is suggested that non-Newtonian properties of the liquid account for the observations. It is shown that the rate of orientation of a particle would then be independent of its size, and this prediction is verified experimentally. Other experimental evidence in support of this suggestion is also described. Some remarks are also made about the possible effect of collisions between the particles when more than one particle is present. © 1956, Cambridge University Press. All rights reserved.

Description: This paper is concerned with the motion in water of air bubbles whose equivalent spherical radii are in the range 0.5-4.0 mm. These bubbles are not spherical but are, approximately, oblate spheroids; and they may rise steadily in a vertical straight line, or along a zig-zag path, or in a uniform spiral. The rectilinear motion occurs when the radius is less than about 0.7 mm, and the other motions occur for larger bubbles. There is disagreement in the literature as to whether it is the zig-zag or the spiral motion that occurs. It was found experimentally that, when the bubbles are produced in the manner described in this paper, only the zig-zag motion occurs when the radius of the bubble is less than about 1 mm, but bubbles of larger radius either zig-zag or spiral depending upon various factors. The spiralling bubble is treated theoretically by assuming that the flow near the front of the bubble is inviscid (the Reynolds number of the motion is several hundred) and considering the distribution of pressure over the front surface. Equations are obtained relating the geometrical parameters of the spiral, the shape of the bubble and the velocity of rise. The analysis is simplified by assuming that the pitch of the spiral is large compared with its radius, and the velocity of rise and shape of the bubble are determined as functions of the radius. The experimental and theoretical values are compared, and fair agreement found. Reasons to account for the disagreement are proposed. A modification of the theory is proposed to take account of the presence of impurities or surface-active substances in the water, and the velocities of rise thus predicted are in agreement with the experimental observations. The zig-zag motion is treated in a similar way, and the analysis leads to an equation which determines the stability of the rectilinear motion. The value of the Weber number at which the rectilinear motion. The value of the Weber number at which the rectilinear motion becomes unstable is deduced, and is found to be in fair agreement with experiment. The experimental evidence on the wake behind solid bodies is described briefly, and reasons are given for suggesting that the zig-zag motion is due to an interaction between the instability of the rectilinear motion and a periodic oscillation of the wake. © 1956, Cambridge University Press. All rights reserved.

Description: 1. The weights at birth of 822 pairs of twin lambs have been studied with respect to the differences between males and females. Data were obtained during five lambing seasons from various breeds and crosses in five flocks.2. The sex distribution of twin pairs came close to the ratio .3. Analyses made within season and within the major breed categories showed that sex differences were small relative to other sources of variation, but that there was a significant effect of sex of co-twin on birth weight. The following average differences were found (the sex of co-twin being indicated in brackets):These differences had an average S.E. of 0·078 lb. (Table 3). The sex difference in litters of mixed sex was twice as large as that obtained from like-sexed litters.4. The data for particular flocks and seasons suggest that in addition to these average effects, there may be some interaction between sex and breed or season which can cause deviations from the averages.5. These results are interpreted to mean that there is competition between twins for some element of growth in limited supply; and that in twins of mixed sex, the result tends to favour the male.