The slower propagation of light in gas or water than in air or vacuum may be attributed to a greater density, or to a less rigidity, in the former case; or we may adopt the more complicated supposition that both these quantities vary, subject only to the condition which restricts the ratio of velocities to equality with the known refractive index.
The density of population is 85.38 per sq.
The accepted atomic weight is accordingly double the density, i.e.
The Hrault average density of population in France is about 190 Ille-et-Vil to the square mile, the tendency being for the large Indre towns to increase at the expense of the small towns Indre-et-I as well as the rural communities.
The average density increased from 257.21 per sq.
The stratification, which may be concentric or excentric, appears to be due to a difference in density of the various layers.
The outer layers are denser than the inner, the density decreasing more or less uniformly from the outside layers to the centre of hilum.
One half of the earth has therefore a greater density than the other.
The distribution of the mass of the atmosphere over the surface of the earth is also controlled by the relief of the crust, its greater or lesser density at the surface corresponding to the lesser or greater elevation of the surface.
Considering the average density of population within the political limits of countries, the following list is of some value; the figures for a few smaller divisions of large countries are added (in brackets) for comparison: Average Population on i sq.
At 524° Dumas deduced the structure S6 from vapour-density determinations, whilst for the range 860 0 to 1040 0, Sainte-Claire Deville and Troost deduced the formula S2.
It will be observed that Belgium leads all the countries of the world in what may be called its railway density, with the United Kingdom a far-distant second in the list, and Persia last.
Viscosity increases with density, but oils of the same density often vary greatly; the coefficient of expansion, on the other hand, varies inversely with the density, but bears no simple relation to the change of fluidity of the oil under the influence of heat, this being most marked in oils of paraffin base.
The connective tissue of the integument and basement membrane imperceptibly merges into that which surrounds the muscular bundles as they are united into denser and definite layers, and this is especially marked in those forms (Akrostomum) where the density of the muscular body-wall has considerably diminished, and the connective tissue has thus become much more prominent.
For example, the physicist determines the density, elasticity, hardness, electrical and thermal conductivity, thermal expansion, &c.; the chemist, on the other hand, investigates changes in composition, such as may be effected by an electric current, by heat, or when two or more substances are mixed.
He burned phosphorus in air standing over mercury, and showed that (1) there was a limit to the amount of phosphorus which could be burned in the confined air, (2) that when no more phosphorus could be burned, one-fifth of the air had disappeared, (3) that the weight of the air lost was nearly equal to the difference in the weights of the white solid produced and the phosphorus burned, (4) that the density of the residual air was less than that of ordinary air.
Again, when tungsten hexachloride is converted into vapour it is decomposed into chlorine and a pentachloride, having a normal vapour density, but as in the majority of its compounds tungsten acts as a hexad, we apparently must regard its pentachloride as a compound in which an odd number of free affinities are disengaged.
The oxychloride, bromides, and other compounds were subsequently discovered; here we need only notice Moissan's preparation of the trifluoride and Thorpe's discovery of the pentafluoride, a compound of especial note, for it volatilizes unchanged, giving a vapour of normal density and so demonstrating the stability of a pentavalent phosphorus compound (the pentachloride and pentabromide dissociate into a molecule of the halogen element and phosphorus trichoride).
It is only by paying great attention to the current density that good results are obtained, since metals other than that sought for may be deposited.
According to the law of Avogadro, equal volumes of different gases under the same conditions of temperature and pressure contain equal numbers of molecules; therefore, since the density depends upon the number of molecules present in unit volume, it follows that for a comparison of the densities of gases, the determinations must be made under coincident conditions, or the observations reduced or re-computed for coincident conditions.
Experiment, however, showed that while the quotient on the left hand of this equation was fairly constant for a great number of substances, yet its value was not gR but 7 R; this means that the critical density is, as a general rule, 3.7 times the theoretical density.
The connexion between the density and chemical composition of solids has not been investigated with the same completeness as in the case of gases and liquids.
The pioneer work in this field, now frequently denominated " spectro-chemistry," was done by Sir Isaac Newton, who, from theoretical considerations based on his corpuscular theory of light, determined the function (n 2 - 1), where n is the refractive index, to be the expression for the refractive power; dividing this expression by the density (d), he obtained (n 2 - i)/d, which he named the " absolute refractive power."
Making this substitution, and dividing by d, the density of the substance, we obtain a/d = (N 2 - I)/(N2+2)d.
For example, boracite forms pseudo-cubic crystals which become truly cubic at 265°, with a distinct change in density; leucite behaves similarly at about 560°.
The strongest and most reliable hold which the ship has upon the whale when moored alongside, is by the flukes or tail; and as from its greater density that part is relatively heavier than any other (excepting the side-fins), its flexibility even in death, causes it to sink low beneath the surface; so that with the hand you cannot get at it from the boat, in order to put the chain round it.