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.
(2) The acceleration of the element at the origin is - n 2 sin nt; so that the force which would have to be applied to the parts where the density is D' (instead of D), in order that the waves might pass on undisturbed, is, per unit of volume, (D' - D)n 2 sin nt.
No form of the elastic solid theory is admissible except that in which the vibrations are supposed to be perpendicular to the plane of polarization, and the difference between one medium and another to be a difference of density only (Phil.
As Lord Kelvin has shown (Baltimore Lectures, p. 304, 1904) (16) may also be obtained by the consideration of the mean density of the altered medium.
If V be the potential, p the density of free electricity at a point in the atmosphere, at a distance r from the earth's centre, then assuming statical conditions and neglecting variation of V in horizontal directions, we have r2 (d/dr) (r 2 dV/dr) - - 4.rp = o.
The density of population is 85.38 per sq.
The density of helium has been determined by Ramsay and Travers as 1.98.
The accepted atomic weight is accordingly double the density, i.e.
(-268.7° C.), the density of the liquid 0.154, the critical temperature 5° abs., and the critical pressure 2.3 atmospheres (Communications from the Physical Laboratory at Leiden, No.
M., and a population (1901) of 278,119, showing an increase of 49% in the decade and a density of 104 inhabitants to the square mile.
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.
There is no doubt that under average conditions of atmospheric density, the .005 should be replaced by 003, for many independent authorities using different methods have found values very close to this last figure.
In cases where the density of the air is not of average value, as on a high mountain, or with an exceptionally low barometer for example, an allowance must be made.
The cadmium molecule, as shown by determinations of the density of its vapour, is monatomic. The metal unites with the majority of the heavy metals to form alloys; some of these, the so-called fusible alloys, find a useful application from the fact that they possess a low melting-point.
The average density increased from 257.21 per sq.
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.
But under the influence of the rotation the parts of greater density tend to recede further from the axis than the parts of less density.
It exhibits in a marked degree the density ol species which, as already pointed out, is explicable by the arrest 01 further southern expansion.
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.
Love has shown that the great features of the relief of the lithosphere may be expressed by spherical harmonics of the first, second and third degrees, and their formation related to gravitational action in a sphere of unequal density.'
The maximum density of population which a given region can support is very difficult to determine; it depends partly on the race and standard of culture of the people, partly on the nature and origin of the resources on which they depend, partly on the artificial burdens imposed and very largely on the climate.
Density of population is measured by the average number of people residing on a unit of area; but in order to compare one part of the world with another the average should, strictly speaking, be taken for regions of equal size or of equal population; and the portions of the country which are permanently uninhabitable ought to be excluded from the calculation.'
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.
There is, however, a tendency for people to remain rooted to the 2 See maps of density of population in Bartholomew's great largescale atlases, Atlas of Scotland and Atlas of England.
From this he was led to the final value of 6.566 for the mean density of the earth as compared with that of water (Phil.
The country is divided into 19 departments, the area and the population of which, according to the census of 1908, are given in the subjoined table: The average density of population on the above figures is 12.9 per sq.
Biltz (Ber., 1888, 21, p. 2013; 1901, 34, p. 2490) showed that the vapour density decreased with the temperature, and also depended on the pressure.
The density of solid sulphur is 2 062 to 2'070, and the specific heat 0.1712; it is a bad conductor of electricity and becomes negatively electrified on friction.
A solution of the free acid may be obtained by decomposing the barium salt with dilute sulphuric acid and concentrating the solution in vacuo until it attains a density of about 1.35 (approximately), further concentration leading to its decomposition into sulphur dioxide and sulphuric acid.
The solution obtained may be evaporated in vacuo until it attains a density of 1.46 when, if partially saturated with potassium hydroxide and filtered, it yields crystals of potassium pentathionate, K 2 S 5 0 6.3H 2 0.
Province Or Government European Russia - Archangel Astrakhan Bessarabia Chernigov Courland Don Cossacks' territory Ekaterinoslav Esthonia Grodno Kaluga Kazan Kiev Kostroma Kovno Kursk Kharkov Kherson Poland Kalisz Kielce Lomza Lublin Grand-Duchy of Finland- Abo-Bjbrneborg Kuopio Nyland Caucasia- Kuban Baku Black Sea territory Daghestan Russia in Asia- Turkestan- Transcaspia Western Siberia- Tobolsk Tomsk Eastern Siberia Irkutsk Yakutsk Transbaikalia Yeniseisk Amur Region Amur Maritime Province Sakhalin It has been found, from a comparison of the densities of population of the various provinces in 1859 with the distribution in 1897, that the centre of density has distinctly moved S., towards the shores of the Black Sea, and W., the greatest increase having taken place in the E.
Of trespassers the number killed per mile of line is about as large in England as in America, the density of population and of traffic in Great Britain apparently counterbalancing the laxity of the laws against trespassing in America.
The distance between stations on intra-urban railways is governed by the density of local traffic and the speed desired to be maintained.
Henry Cavendish, from which it appeared that Cavendish, already famous by many other researches (such as the mean density of the earth, the composition of water, &c.), must be looked on as, in his day, a man of Maxwell's own stamp as a theorist and an experimenter of the very first rank.
The density of population in 1900 was 33.5 per sq.
There he made the acquaintance of Thomas Andrews, whom he joined in researches on the density of ozone and the action of the electric discharge on oxygen and other gases, and by whom he was introduced to Sir W.
Owing to difference of density the oil and water in the anticlines separate into two layers, the upper consisting of oil which fills the anticlines, while the water remains in the synclines.
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.
His terminology was vague and provoked caustic criticism from Berzelius; he assumed that all molecules contained two atoms, and consequently the atomic weights deduced from vapour density determinations of sulphur, mercury, arsenic, and phosphorus were quite different from those established by gravimetric and other methods.
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).
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.
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.
The actual values of the topic parameters can then readily be expressed in terms of the elements of the crystals (the axial ratios and angles), the density, and the molecular weight (see Groth, Physikalische Krystallographie, or Chemical Crystallography).
Density, specific heat, &c.) of the original and the resulting modification, a change being in general recorded only when polymorphism exists.
Change of temperature usually suffices to determine this, though in certain cases a variation in pressure is necessary; for instance, sodium magnesium uranyl acetate, NaMg(UO 2) 3 (C 2 H 3 O 2) 9.9H 2 O shows no change in density unless the observations are conducted under a considerable pressure.