its location in terms of latitude and longitude. That the center of population is slightly south and between 4 and 5 miles west of the geographical center is evidence that the western half of the island is more thickly settled than the eastern and the southern half has slightly more residents than the northern.

SEX.

[See Tables V and VI.]

In a total population of 953,243 Porto Rico had 8,721 more females than males, an excess amounting to 0.9 per cent of the total population. In 1887 the excess of females in the de jure population was only 478, and in the de facto population the males were 523 in excess. In 1860 the males outnumbered the females by 9,653, or 1.7 per cent of the total population. It appears thus that the proportion of females is slowly increasing. An excess of that sex was found in six of the seven departments into which the island is divided. The following table gives the absolute excess of males or females in each department and the ratio which this excess bears to the total population of the department:

In no department did the excess of females equal the average excess of males in the island of Cuba (3.6 per cent) or the excess of females found in many other West India islands. As a marked inequality of the two sexes is usually a result and evidence of considerable migration into or away from the district under consideration, so an approximate equality in the numbers of the two sexes, both in the island as a whole and in its several departments, is probably connected with the slight amount of immigration, emigration, or migration within the island, and also with the small urban population, since an urban population usually contains a decided excess of females. The two departments in which the ratio of males was highest are also the two which are growing most rapidly. This may point to some immigration of males to Ponce and Arecibo from other parts of Porto Rico.

When the several municipal districts are examined with regard to the proportion of the two sexes, the three small outlying islands are found to have an excess of males, but among the sixty-eight districts

of Porto Rico proper it appears that the coast districts in rather more cases than the inland and upland districts have an excess of females, as seen by the following table:

Of the inland districts one-half and of the coast districts only about one-fourth, have an excess of males.

In the coast districts 48.5 per cent of the population are male, while in the inland districts 51 per cent are male. The three coast cities, San Juan, Ponce, and Mayaguez, collectively, contain 48.5 per cent of males, or the same as for the coast districts as a whole. The percentage of males, therefore, in the inland districts is perceptibly higher than along the coast.

AGE.

[See Tables VIII and IX.]

Probably the best single and simple expression for the age of a great number of people like the inhabitants of Porto Rico is what is called the median age; that is, the age such that half the members of the population group under consideration are younger and half are older. To compute it accurately, the census tables should present the ages by single years. That information being given, it is easy to ascertain within what single year of life the median age must lie. It is then assumed that within the year of age thus fixed the persons were evenly distributed; in other words, that there were as many persons living in the first tenth of the year as in each other tenth. In this way the median age of the population of the United States in 1890 has been fixed at 21.9 years. The present census of Porto Rico reports ages above 5 not by single years but by periods of years, usually five,' and, accordingly, to get the median age it has been necessary to distribute the population of Porto Rico for one age period to the single years. In so doing it has been assumed that the number of each year of age in that period bears the same proportion to the total in Porto Rico that it does in the United States. The median age in Porto Rico

'The division of the group 15-19 at 17 enables one to know the population of school age, 5-17, and that of age to serve in the militia, 18-44. The division of the group 20-24 at 20 enables one to know the potential voters. The division of the group 0–4 into single years allows a study of the balance between birth rate and death rate during the early years, before it is seriously affected by migration.