principle the surface of a metal is not considered as a region of the same class as the surface of water or an organic liquid, since the characteristics of the two regions are quite unlike. Corresponding to the various empirical relations the following 'normal' values of the entropy may be given: Entropy in ergs per degree per molecule 1. Liquid to surface.... 2. Liquid to vapor at the special concentration of: C = 0.00507 mols per liter... c = 0.0127 mols per liter.. C = 0.0201 mols per liter. (These values become less accurate as the concentration of the vapor in creases.) 3. Solid to vapor at the melting point... X1010 2.96 .18.8 .16.7 .15.7 4. Solid to liquid....... 5. Solids dissociate to 760 mm. vapor pressure. .21.0 9.0 .22.0 Of these the first is the most exact, the second holds moderately well under the conditions imposed, and the fourth, as might be expected, is one of the least accurate. Walden's rule is that the molar heat of fusion divided by the temperature is equal to 13.5 calories per degree for normal substances, or the molar entropy of fusion has the given value. This rule Walden' found to hold for a large number of organic substances. When the data did not correspond with what should be obtained according to the rule, Walden assumed that it still remains valid, but that the molecular weight is different from that given by the formula. However it is evident that this explanation is not sufficient to account for all of the deviations which exist. 8 At my request Mr. L. E. Roberts has studied practically all of the available data on the entropy of melting, and has found the general relations which hold. One of the greatest obstacles in this connection is that the data are in many cases extremely inaccurate. They indicate that the latent heat of melting of a metallic element which crystallizes in the regular system, increases as the melting point rises, and the entropy averages about 2.2 calories per gram atom per degree. The salts show a somewhat similar relation, and at the same time there seems to be a general increase in the entropy of fusion with the number of gram atoms in the formula weight of the salt. There is a great deal of irregularity, but for the halogen salts the entropy is of the order of 2.2 calories per degree per gram atom, or about the same value as is found for the metals. Hydrogen, hydroxides and water of crystallization are represented by lower values. Thus the entropy of fusion of the hydroxides of sodium, potassium, rubidium, and caesium, is about 2.8 calories per degree per gram molecule. On turning to molecular compounds such as ammonia and carbon dioxide it is found that the entropy of fusion is 9.3 for the former and 8.9 for the latter, while for benzene the value is 8.3. Corresponding to Walden's rule a large number of organic compounds have entropies of fusion between 12 and 14 calories per degree, while many of the substances with smaller entropies of fusion possess other properties characteristic of associated liquids when they are in the liquid state. As might be expected substances with very complex formulae give high values, the increase with molecular complexity being very distinct. Thus with stearic acid (CH36O2) the value rises to 40, while the acid with two carbon atoms has an entropy of only 9.5, with nine carbon atoms of 10.5, while in the case of the 12 carbon atom acid the value rises to 27. It is thus to be seen that the entropy is a very important function in a study of the transfer of molecules from one region to another, and that in general the price which a molecule has to pay in terms of energy in order to undergo any certain change, increases with the temperature or the molecules pay in proportion to their wealth with respect to energy. There is also an increase in this energy price whenever the complexity of the molecules increases sufficiently. The price in terms of entropy is much more constant than the price in terms of energy, and in this sense there is an analogy to the action of a Carnot engine. It is believed that the point of view presented in abstract in this short paper will greatly change the present attitude in regard to the determination of molecular association in liquids, and it is possible that it may be of importance in a study of the general subject of the partition of energy, as well as in changes of kinetic into potential energy." 10 The complete paper of which this is a part will be presented to the Journal of the American Chemical Society by Mr. L. E. Roberts and the writer, for publication in a later issue. 1 J. Amer. Chem. Soc., Easton, Pa., 38, 1916, (1452). 2 Ibid., 41, 1919, (970-92). PROCEEDINGS, May, 1919. Physic. Rev., July, 1919. 4 Leipzig, Ann. Physik, 27, 1886, (452). 5 London, Phil. Trans. Roy. Soc., 184A, 1893, (647), Zs. Physik. Chem., Leipsig, 12, 1893, (647). 6 J. Amer. Chem. Soc., 37, 1915, (975). 7 Zs. Elektrochem., 14, 1908, (715). 8 Crompton, J. Chem. Soc., 67, 1895, (315-327). T. W. Richards, J. Franklin Institute, 1902. 'Wayling, Phil. Mag., 37, 1919, (495). 10 Since this paper was submitted I have received a copy of a paper presented to the Société Française de Physique by M. J. Duclaux on June 6, 1919. He believes that there are quantities of energy of magnitude 6.6 X 10-16 ergs. THE DISPLACEMENT OF THE GRAVITATING NEEDLE IN ITS DEPENDENCE ON ATMOSPHERIC TEMPERATURES BY CARL BARUS DEPARTMENT OF PHYSICS, BROWN UNIVERSITY Communicated October 8, 1919 1. Introductory.-In Science (50, pp. 214, 279, 1919) I communicated some of the early results, showing that the deflection of the needle of a gravitation apparatus varies in marked degree with the temperature on the outside of the building. I have since carried these experiments on for another month and the evidence has become more definitely interpretable. The work was done in a semi-subterranean room, in which the thermostat shows temperature variations which do not usually exceed a fraction of a degree. The room is large and so damp that all electrical excitation is excluded. Tests with radium fully confirmed this. Moreover the room is kept dark. The apparatus (PROCEEDINGS, 4, p. 338, 1918) placed on the north-south wall of the pier confronts an eastern 30-inch wall, at a distance of about 4 meters and the outside of this is illuminated by sunlight, if present, in the morning, only. = 2. Observations.-The observations during July and August are given at the bottom of the figure, the two curves being mean results of the a.m. and p.m. readings, respectively. The telescopic reading of the scale is y, so that Ay denotes the mean (static) excursion or double amplitude, when the attracting mass, M = 1 kgm. is passed from one side to the other of the attracted shot (m 0.6 gram), at the end of a needle suspended by a quartz fiber. The actual excursion of the shot is Ax = 0.01455 Ay, so that the magnification is about 70. The figure shows that even these mean excursions vary enormously, from values much below Ay = 2 to values above 7, easily five times. If individual excursions were taken, ratios as high as 10 might be found, in spite of the practically constant room temperature. On the upper part of the chart I have inserted the temperature observations in degrees F., made at Providence by the United States Weather Bureau, as well as the temperature variations A0 (high minus low) of the successive days of the months, the same abscissas holding for all curves. In the earlier data there seemed to be a close association between the Ay and curves. In the present data the regions a, b, c, d, e, belong together, though the Ay curve follows the curve with a lag of one or more days. A far better agreement in sense, not quantitatively always, now appears between the Ay and ▲0 curves, and here in the given time scale, practically without a lag. To bring this to the eye more clearly, I have indicated the corresponding successive cusps in both curves with the same numbers 1 to 23. The agreement is in fact as close as it can possibly be, remembering that 40 holds for twenty-four hours of the day and Ay only for the daylight interval of observation. In the same way the a.m. and p.m. curves differ enormously when there is sunlight, and very little in damp cloudy rainy weather (R in curve). In general and apart from details, the a.m. excursions reappeared in a subdued form in the p.m. results. 3. The needle in vacuum.-In Science I also communicated a series of results since much amplified, showing that for a case of two glass plates spaced by an impregnated wood frame, the initial attractions could be diminished to about one-third of their value by exhausting the case. The excursions diminished with the pressure, at a mean rate of 1%, per mercury centimeter of pressure. The glass plates in this case were about 1.8 cm. apart, inside. In case of the plenum the general character of the a.m. and p.m. excursion did not essentially differ from the graphs for apparatus I. With the object of gaining some insight into the remarkable behavior at low pressure a new apparatus (no. III) was constructed with the glass plates spaced by a rectangular frame made of square brass tubing. The inside distance between plates was here 1.3 cm.; but in other respects it closely resembled the wood frame specified. The results with this metal case, however, differed totally from those of the other. In the morning of a bright day, there was usually marked repulsion between M and m, which changed gradually into an attraction at the close of the day. The repulsion was often so strong that the ends of the needle were pushed up into contact with the glass plates, to which position they returned whenever removed by tapping. It was found, however, that the needle could be immediately freed by exhaustion of the case. In other words the repulsions passed continuously into attractions which were here at their maximum at the highest 2 3 exhaustions. The behavior of the metal case was thus the reverse of that of the wood case. In the former exhaustion removed a repulsion; in the latter, an attraction. It is difficult to assign a reason for this as there are three forces in contention: viz., gravitation and the radiant forces of the case (static) and of the external mass M. One is tempted to contrast the non-conducting wood with the conducting metal. The greater narrowness of the frame of the latter, however, gives the forces due to temperature distributions an advantage. In one respect the exhausted metal case has shown marked superiority; at a definite high vacuum, the excursions of the needle on any day are without drift; they are nevertheless variable on successive days. It is thus also improbable that this vacuum excursion corresponds to the gravitational attraction, so that an adequately trustworthy excursion is yet in arrears. 4. Record of the vacuum needle.-To exhibit these relations more clearly I have constructed figure 2, which contains a record of mean |