Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/533

Rh must be of great antiquity. There have been only two or three moderate during the, though  continually issues from the , and from time to time vast showers of  and s are shot up.

1em  POPPÆA SABINA. See.  POPPY OIL is obtained by from the minute of the  or, Papaver somniferum (see,  ). The white-ed and black-ed varieties are both used for ; but, when the production of is the principal object of the, the black  is usually preferred. The qualities of the yielded by both varieties and the proportion they contain (from 50 to 60 per cent.) are the same. By cold s of fine quality yield from 30 to 40 per cent. of virgin or white oil (huile blanche), a transparent  with a slight yellowish tinge, bland and pleasant to, and with almost no perceptible. On second with the aid of  an additional 20 to 25 per cent. of inferior (huile de fabrique or huile russe) is obtained, reddish in, possessed of a  , and a -like. The belongs to the  or, having as its principal constituent ; and it possesses greater  power than raw. Its at 15° is 0·925; it remains  at −15°, but forms a thick white  at −20°, which does not again become  till the  rises to −2° Poppy  is a valuable and much used medium for. The fine qualities are largely used in the north of (huile de œillette) and in  as a , and are less liable than  to. The absence of and characteristic  in poppy  also leads to its being much used for. The inferior qualities are principally consumed in and, and for  in. The is very extensively used in the  of the  and other  regions for  and domestic purposes. By methods in  about 30 per cent. of is extracted, and the remaining   is used as  by the. Ordinary poppy- is a valuable  material, rich in ous constituents, with an  showing an unusually large proportion of. The of the yellow horned poppy, Glaucium luteum, yields from 30 to 35 per cent. of an having the same  and other properties as poppy ; and from the Mexican poppy, Argemone mexicana, is obtained a non-   useful as a  and for.  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 governing the forces whose joint action has produced population, will receive attention.

I. Population, statically considered, may be defined as “the totality of existing within a at a .” 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. The totality just mentioned is ascertained in and by  s by the  operation known as the. It is usual to obtain by means of a a good deal of information beyond the bare fact of the number of  whose existence is, for the purposes of the, taken cognizance of. Part of this information is obtained for purposes connected with the of the, such as that contained in replies to questions as to the , , &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 and. A which did not distinguish between the number of  and the number of  composing the population of which it takes cognizance would be seriously defective. Inquiries as to the and the girth round the  of individuals are usually made in  where, and the degree of prevalence of , such as  and , 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. The of each individual is, however, easily obtained in the course of the operations of the. We shall now briefly set forth the general characteristics of a population, examined at a and without reference to similar phenomena at.

Population of the .—The total population of the is, to a large extent, an estimate, inasmuch as in some a proper  has never been taken, while in many the interval that has elapsed since the last  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, 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 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 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 advances the area of the unknown or partially known, which is at present large, will gradually diminish.

—Estimates of the Population of the.

