The cause of the continuous though varying decrease which these figures reveal has been emigration. This movement of population took its first great impulse from the famine of 1846 and has continued ever since. When that disaster fell upon the country it found a teeming population fiercely competing for a very narrow margin of subsistence; and so widespread and devastating were its effects that between 1847 and 1852 over 1,200,000 of the Irish people emigrated to other lands. More than 1,000,000 of these went to the United States of America, and to that country the main stream has ever since been directed. Between 1851 and 1905 4,028,589 emigrants left Ireland—2,092,154 males and 1,936,435 females, the proportion of females to males being extraordinarily high as compared with the emigration statistics of other countries. Between these years the numbers fluctuated widely—1852 showing the highest total, 190,322 souls, and 1905 the lowest, 30,676 souls. Since 1892, however, the emigrants in any one year have never exceeded 50,000, probably because the process of exhaustion has been so long in operation. As Ireland is mainly an agricultural country the loss of population has been most marked in the rural districts. The urban population, indeed, has for some years shown a tendency to increase. Thus in 1841 the rural population was returned as 7,052,923 and the urban as 1,143,674, while the corresponding figures in 1901 were respectively 3,073,846 and 1,384,929. This is further borne out by the percentages given in the above table, from which it will be seen that the greatest proportional decrease of population has occurred in the two provinces of Munster and Connaught, which may be regarded as almost purely agricultural. That the United States remained the great centre of attraction for Irish emigrants is proved by the returns for 1905, which show that nearly 80% of the whole number for the year sailed for that country. Ireland does little to swell the rising tide of emigration that now flows from England and Scotland to British North America.
Turning now to the census figures of 1901, we find that the population had diminished as compared with 1891 by 245,975. During the decade only three counties, Dublin, Down and Antrim, showed any increase, the increase being due to the growth of certain urban areas. Of the total population of 4,458,775, 2,200,040 were males and 2,258,735 were females. The inhabitants of the rural districts (3,073,846) decreased during the decade by over 380,000; that of the urban districts, i.e. of all towns of not less than 2000 inhabitants (1,384,929) increased by over 140,000. This increase was mainly due to the growth of a few of the larger towns, notably of Belfast, the chief industrial centre of Ireland. Between 1891 and 1901 Belfast increased from 273,079 to 349,180; Dublin from 268,587 to 289,108; and Londonderry, another industrial centre in Ulster, from 33,200 to 39,873. On the other hand, towns like Cork (75,978), Waterford (26,743) and Limerick (38,085), remained almost stationary during the ten years, but the urban districts of Pembroke and of Rathmines and Rathgar, which are practically suburbs of Dublin, showed considerable increases.
From the returns of occupation in 1901, it appears that the indefinite or non-productive class accounted for about 55% of the entire population. The next largest class was the agricultural, which numbered 876,062, a decrease of about 40,000 as compared with 1891. The industrial class fell from 656,410 to 639,413, but this represented a slight increase in the percentage of the population. The professional class was 131,035, the domestic 219,418, and the commercial had risen from 83,173 in 1891 to 97,889 in 1901. The following table shows the number of births and deaths registered in Ireland during the five years 1901-1905.
| Births. | Deaths. | |
| 1901 | 100,976 | 79,119 |
| 1902 | 101,863 | 77,676 |
| 1903 | 101,831 | 77,358 |
| 1904 | 103,811 | 79,513 |
| 1905 | 102,832 | 75,071 |
The number of illegitimate births is always very small in proportion to the legitimate. In 1905 illegitimate births numbered 2710 or 2.6 of the whole, a percentage which has been very constant for a number of years.
Railways.—The first act of parliament authorizing a railway in Ireland was passed in 1831. The railway was to run from Dublin to Kingstown, a distance of about 6 m., and was opened in 1834. In 1836 the Ulster railway to connect Belfast and Armagh, and the Dublin and Drogheda railway uniting these two towns were sanctioned. In the same year commissioners were nominated by the crown to inquire (inter alia) as to a general system for railways in Ireland, and as to the best mode of directing the development of the means of intercourse to the channels whereby the greatest advantage might be obtained by the smallest outlay. The commissioners presented a very valuable report in 1838, but its specific recommendations were never adopted by the government, though they ultimately proved of service to the directors of private enterprises. Railway development in Ireland progressed at first very slowly and by 1845 only some 65 m. of railway were open. During the next ten years, however, there was a considerable advance, and in 1855 the Irish railways extended to almost 1000 m. The total authorized capital of all Irish railways, exclusive of light railways, at the end of 1905 was £42,881,201, and the paid-up capital, including loans and debenture stock, amounted to £37,238,888. The total gross receipts from all sources of traffic in 1905 were £4,043,368, of which £2,104,108 was derived from passenger traffic and £1,798,520 from goods traffic. The total number of passengers carried (exclusive of season and periodical ticket-holders) was 27,950,150. Under the various acts passed to facilitate the construction of light railways in backward districts some 15 lines have been built, principally in the western part of the island from Donegal to Kerry. These railways are worked by existing companies.
The following table shows the principal Irish railways, their mileage and the districts which they serve.
| Name of Railway. | Mileage. | Districts Served. |
| Great Southern & Western | 1083 | The southern half of Leinster, the whole of Munster, and part of Connaught, the principal towns served being Dublin, Cork, Waterford, Limerick and Sligo. |
| Midland Great Western | 538 | The central districts of Ireland and a great part of Connaught, the principal towns served being Dublin, Athlone, Galway and Sligo. |
| Great Northern | 533 | The northern half of Leinster and a great part of Ulster, the principal towns served being Dublin, Belfast, Londonderry, Dundalk, Drogheda, Armagh and Lisburn. |
| Northern Counties1 (now owned by the Midland Railway of England) | 249 | The counties of Antrim, Tyrone and Londonderry. |
| Dublin & South Eastern2 | 161 | The counties of Dublin, Wicklow, Wexford and Waterford. |
| Donegal | 106 | The counties of Tyrone and Donegal. |
| Londonderry & Lough Swilly | 99 | The counties of Londonderry and Donegal. |
| Cork, Bandon & South Coast | 95 | The counties of Cork and Kerry. |
| Belfast & County Down | 76 | The county of Down. |
1 Formerly Belfast and Northern Counties.
2 Formerly Dublin, Wicklow and Wexford.
There is no lack of cross-channel services between Ireland and Great Britain. Belfast is connected by daily sailings with Glasgow, Ardrossan, Liverpool, Feetwood, Barrow and Heysham Harbour, Dublin with Holyhead and Liverpool, Greenore (Co. Down) with Holyhead, Larne (Co. Antrim) with Stranraer, Rosslare (Co. Wexford) with Fishguard and Kingstown (Co. Dublin) with Holyhead.