Notices of the proceedings at the meetings of the members of the Royal Institution of Great Britain with abstracts of the discourses . hrough a tube. Fig. 5 is intended to show how a small quantity of the material,included between two near planes, lies after a short time. A smallcube of the material is shown in the initial stage and its subsequentshape when drawn out. The connection will thus be appreciatedbetween the kind of movement here taking place, and that consistentwith the definition of viscosity as illustrated by the model. The rate of elongation of the rod divided by the tension give
Notices of the proceedings at the meetings of the members of the Royal Institution of Great Britain with abstracts of the discourses . hrough a tube. Fig. 5 is intended to show how a small quantity of the material,included between two near planes, lies after a short time. A smallcube of the material is shown in the initial stage and its subsequentshape when drawn out. The connection will thus be appreciatedbetween the kind of movement here taking place, and that consistentwith the definition of viscosity as illustrated by the model. The rate of elongation of the rod divided by the tension gives usa coefficient of viscous traction. We have every reason to expectthis to be about three times the viscosity of the material, and ex-periment supports this view. The value of the viscosity of pitch Fig. 5. 490 Professor F. T. Trouton [March 11, found in this way is shown in the table. The agreement with thevalues found by other methods is satisfactory for experiments of thischaracter. Bending of Bars. When a bar of pitch is laid horizontally, supported only at itsends, it sags in the middle. In doing so the upper parts of the. A Fig. 6. material become compressed, while the lower are drawn out. Thisis shown in Fig. 6. Two little squares are put in to help us to under- DcflcSi-on. af Viscous Beam ?Pitch Fig. 7. stand the movement of the material; these are subsequently trans-formed into the skew shape we have seen to be associated withviscous flow. 1904.] on the Motion of Viscous Substances. 491 The upper square is compressed horizontally, the lower is drawnout in the same direction. Experiment shows that the rate at which the bar falls at its centreis approximately that given by theory based on similar suppositionsto tho-e which were made in the case of traction. Fi ;. 7 shows the time which, according to the theory, should betaken by rods of different lengths in falling at their centres throughthe same distance. The shorter the bar the slower it falls. Themarked points are
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