I obtained similar results for other solid bodies, as platinum According to these researches the edge-angle appears to increase a little with an augmenting concentration of the saline solution, but otherwise to differ only inconsiderably from the edge-angle of pure water. 8. Besides the direct methods described in the preceding paragraphs, I have also simultaneously determined the edgeangle indirectly against the same solid substances from the form of flat air-bubbles, Upon the same surfaces of glass and silver, which were cleansed with alcohol, water, and a clean linen cloth, I found by both methods the following values of the edge-angle for mixtures of alcohol and water of various specific gravities:— With the exception of the one determination in the case of very dilute alcohol and silver, where the fluid surface of the air-bubble was very difficultly movable, and a casual impurity may have produced a difference, the results of both methods of observation agree as far as can in general be expected in these investigations. 9. The magnitude of the surface-tension a12 at the boundary of a solid and of a liquid may be determined to within an additive constant so soon as the tension of the free surface, and the edge-angle for various liquids upon the same solid (for example glass), are known. From equation (5), § 1, we have for the fluids 2 and 3 :— Call h the mean height of ascent in capillary tubes of diameter 2r for a liquid of specific gravity; then, from equation (9), a2 cos 02=(a)=rh1⁄2, whence follows at once the capillary constant (a) of the free surface of the liquid concerned, as it used formerly to be calculated from the height of capillary ascent in glass tubes under the assumption that the edge-angle was zero. Moreover the value of a, cos 0, may also be calculated from observations on flat air-bubbles beneath a level plate of glass. Comparing 12 for various liquids with for water as fluid 3, we obtain the following values from my earlier observations * : In this Table the liquids are arranged according to the value of their surface-tension at the boundary of glass, as follows from the observations upon capillary tubes. With the exception of mercury, the bounding-surface of glass and alcohol exhibits the greatest, and that of glass and water the smallest surface-tension. Instead of which we may also say alcohol has the least, water the greatest adhesion to glasst. A similar calculation may be carried out in the case of all the aqueous saline solutions for which I have lately established the values of a. According to equation (5c), in the case of all saline solutions for which (a) increases with augmented concentration, the surface-tension of the common bounding surface of glass and saline solution will be the less, and the adhesion of the saline solution to the glass will be the greater, as the saline solution is the more concentrated. This occurs for all the substances investigated by me, with the exception of hydrochloric acid, nitric acid, and ammonia; and it holds also for alcoholic solutions of chloride of lithium and chloride of calcium§. Besides, the same quantity 12 may be calculated in Pogg. Ann. cxxxix. p. 15 (1870); and Phil. Mag. [IV.] vol. xli. No. 273 (April 1871). For melted glass I have found (Pogg. Ann. cxxxv. p. 642, 1868) a=18.09 mgr.; and since this value was necessarily obtained with a lowering temperature, there is nothing astonishing in the value >34.53, as follows from equation (5 A) and the observations on mercury. According to this equation, a, must always he greater than a value of a, cos 0. Pogg. Ann. clx. pp. 371-374 (1877), table xi. § Loc. cit. p. 566, Phil. Mag. S. 5. Vol. 5. No. 32. May 1878. Ꮓ yet another way from the observation of flat bubbles or drops of one liquid 2 in another liquid 3 or 4, beneath or upon a glass plate. From equation (4), olive-oil α11-13=23 COS 03-α24 COS 04. Let the flat glass correspond to the solid...... 1, liquid 2, ... ... 3 (5D) then according to my earlier observations*, a23=2.096 mgr., 03 =17°, a24=0·226 mgr., α14-α13=2·001 mgr. −0·009 mgr.; or if the boundary of glass and water a13 α14-x=1.992 mgr. is called x, According to this investigation also, the surface-tension of the level bounding surface of glass and alcohol is therefore greater than that of glass and water. If water be taken as fluid 3, and the various liquids of observations Nos. 2, 10-14, & 16 of the former researches mentioned†, as fluid 2, then the surface-tension of the common boundary of glass and the liquid concerned may be calculated from equation (5 D), except an additive constant a13, or x. The figures of the last columns in both Tables VIII. and IX. Pogg. Ann. cxxxix. p. 27 (1870); and Phil. Mag. [IV.] vol. xli. p. 263 (April 1871). † Ibid. should be identical; likewise the order of succession of the liquids. Neither is the case; and so far the theory is not in harmony with experience. a It must, indeed, be remembered that the values of the edgeangle were only determined approximately with flat bubbles and drops, and can lay no claim to great accuracy-that the magnitude of the free surface of the glass may have had different values in the various researches in consequence of impurities (see § 12, hereafter)—and, finally, that merely the presence of a fluid may alter the molecular nature and therefore also the surface-tension of another, so that the density of a surface bounded by air may be quite different from that of one bounded by another fluid (compare § 11). [To be continued.] XLVII. The Production of Thermoelectric Currents in Wires subjected to Mechanical Strain. By G. W. VON TUNZELMANN, Holder of the Clothworkers' Exhibition in Chemistry and Physics at University College, London*. 6 THE following inquiry was suggested by some observations recorded in a paper of Sir William Thomson's on the Electrodynamic Qualities of Metals, in the Philosophical Transactions for 1856; and the object in view was to investigate the conditions under which thermoelectric currents are produced in a circuit composed of a single metal when one portion of the metallic conductor is subjected to a strain and the junctions of the strained and unstrained portions are maintained at different temperatures. The experiments were made upon wires of iron, steel, and copper, the copper wire employed having been obtained from Messrs. Johnson, Matthey & Co. as chemically pure. Two tin cans were obtained open at the top, and pierced at the bottom by necks into which india-rubber corks were inserted; and through slits in these the wires were passed. The wire was fastened by a clamp in the lower can, and was grasped in the upper one by a pair of wire-drawing dogs attached to the shorter arm of a lever, to the longer arm of which was attached the weight by which the strain was produced. the earlier experiments ordinary weights were used; but ultimately these were rejected, as it was found impossible to apply and remove them in a sufficiently gradual manner to prevent a certain amount of shock, which introduced complications. Communicated by the Physical Society. In |