In 1519 Cortes sent a party of ten men to climb a smoking mountain which was evidently Popocatepetl; and in 1522 Francisco Montaño not only reached the summit but had himself let down into the crater a depth of 400 or 500 feet. No second ascent of the mountain is recorded till April (see Brantz Mayer, Mexico, vol. ii.) and November 1827. Other ascents have been made in 1834, 1848, arid subsequent years.
POPPÆA SABINA. See Nero.
POPPY OIL is obtained by pressure from the minute seeds of the garden or opium poppy, Papaver somniferum (see Opium, vol. xvii. p. 787). The white-seeded and black-seeded varieties are both used for oil-pressing; but, when the production of oil is the principal object of the culture, the black seed is usually preferred. The qualities of the oil yielded by both varieties and the proportion they contain (from 50 to 60 per cent.) are the same. By cold pressure seeds of fine quality yield from 30 to 40 per cent. of virgin or white oil (huile blanche), a transparent limpid fluid with a slight yellowish tinge, bland and pleasant to taste, and with almost no perceptible smell. On second pressure with the aid of heat an additional 20 to 25 per cent. of inferior oil (huile de fabrique or huile russe) is obtained, reddish in colour, possessed of a biting taste, and a linseed-like smell. The oil belongs to the linoleic or drying series, having as its principal constituent linolein; and it possesses greater drying power than raw linseed oil. Its specific gravity at 15° C. is 0·925; it remains limpid at −15° C., but forms a thick white mass at −20° C., which does not again become fluid till the temperature rises to −2° C. Poppy oil is a valuable and much used medium for artistic oil painting. The fine qualities are largely used in the north of France (huile de œillette) and in Germany as a salad oil, and are less liable than olive oil to rancidity. The absence of taste and characteristic smell in poppy oil also leads to its being much used for adulterating olive oil. The inferior qualities are principally consumed in soap-making and varnish-making, and for burning in lamps. The oil is very extensively used in the valley of the Ganges and other opium regions for food and domestic purposes. By native methods in India about 30 per cent. of oil is extracted, and the remaining oleaginous cake is used as food by the poor. Ordinary poppy-oil cake is a valuable feeding material, rich in nitrogenous constituents, with an ash showing an unusually large proportion of phosphoric acid. The seed of the yellow horned poppy, Glaucium luteum, yields from 30 to 35 per cent. of an oil having the same drying and other properties as poppy oil; and from the Mexican poppy, Argemone mexicana, is obtained a non-drying purgative oil useful as a lubricant and for burning.
POPULATION. The phenomena of population are the product of physical forces the nature of which it will be necessary to investigate. It will, however, be convenient to consider population, in the first place, as a statical phenomenon, that is, to observe and classify the principal features it presents, without attempting to investigate the system of causes of which they are the effects. Thereafter the dynamical aspects of the subject, namely, the general laws governing the forces whose joint action has produced population, will receive attention.
I. Population, statically considered, may be defined as “the totality of human beings existing within a given area at a given moment of time.” This definition is identical with that adopted by Haushofer (p. 87), except that that eminent authority thought it unnecessary to add the clause relating to time. The totality just mentioned is ascertained in modern times and by civilized nations by the statistical operation known as the Census (q.v.). It is usual to obtain by means of a census a good deal of information beyond the bare fact of the number of persons whose existence is, for the purposes of the census, taken cognizance of. Part of this information is obtained for purposes connected with the administration of the state, such as that contained in replies to questions as to the religion, profession, &c., of the individuals numbered. But these facts, though highly important, are not facts of population strictly speaking. There are two very important characteristics common to all considerable populations—namely, the approximate constancy of the distribution of the population as regards sex and age. A census which did not distinguish between the number of male and the number of female persons composing the population of which it takes cognizance would be seriously defective. Inquiries as to the height and the girth round the chest of individuals are usually made in countries where military service is compulsory, and the degree of prevalence of bodily defects, such as blindness and deafness, is also noted for similar reasons; but such inquiries are the work of specialists, official and other, and in any case are not included in the information obtained from a census. The age of each individual is, however, easily obtained in the course of the operations of the census. We shall now briefly set forth the general characteristics of a population, examined at a particular point of time and without reference to similar phenomena at previous points of time.
Population of the World.—The total population of the world is, to a large extent, an estimate, inasmuch as in some countries a proper census has never been taken, while in many the interval that has elapsed since the last operation is so long as to reduce it to the level of serving as a basis for a calculation in which estimates play a large part. So great, indeed, is the uncertainty in which all such calculations are involved that an eminent French statistician, M. Block, abandons all attempt to deal with the problem, dismissing the subject in the following note (Traité, &c., p. 401),—“Nous abstenons de donner le chiffre de l’ensemble de la population de la terre; personne ne connait ce chiffre.” With this view of the matter we entirely agree, without, however, any disparagement to the valuable work done by Behm and Wagner, who have made the population of the earth their special study, and are under no illusions as to the accuracy of the results they have to offer. The work of these two eminent men of science has at any rate drawn attention to the lacunæ, in our present knowledge, besides arranging and co-ordinating the great multiplicity of well-ascertained facts at our disposal. As civilization advances the area of the unknown or partially known, which is at present large, will gradually diminish.
| Author of Estimate | Year. | Number (in Millions). |
| Riccioli | 1660 | 1,000 |
| Süssmilch | 1742 | 950–1,000 |
| Voltaire | 1753 | 1,600 |
| Volney | 1804 | 437 |
| Pinkerton | 1805 | 700 |
| Fabri | 1805 | 700 |
| Malte-Brun | 1810 | 640 |
| Morse | 1812 | 766 |
| Graberg v. Hemsö | 1813 | 686 |
| Balbi | 1816 | 704 |
| Reichard | 1822 | 732 |
| Hassel | 1824 | 938 |
| Stein | 1833 | 872 |
| Fränzl | 1838 | 950 |
| V. Rougemont | 1838 | 850 |
| Omalius d’Halloy | 1840 | 750 |
| Bernoulli | 1840 | 764 |
| V. Roon | 1840 | 864 |
| Berghaus | 1842 | 1,272 |
| Balbi | 1843 | 739 |
| Kolb | 1868 | 1,270 |
| Behm and Wagner | 1880 | 1,456 |
| 〃〃 | 1882 | 1,434 |
