There is one matter connected with the volume of immigration which marks the last few years of the modern period and is of the greatest importance. This is the provision for estimating the exact net gain or loss in population each year through immigration movements. Until very recently the only immigration figures which were considered worth while were those of arriving aliens. It was tacitly assumed that our immigrant traffic was a wholly one-sided one. But gradually people began to realize that there was a large countercurrent of departing aliens. In the Report of the Commissioner General of Immigration for 1906 (p. 56) an effort is made to supply as far as possible these data for the years 1890 to 1906. But in the absence of any legislation requiring shipmasters to furnish lists of departing passengers, these figures are admittedly incomplete, and no attempt is made to distinguish aliens from citizens of the United States. The nearest approach that can be made to ascertaining the number of departing aliens is to assume that all the passengers other than cabin belonged to this class. This is probably not very far from the truth, and taking these figures as a guide, we can get some idea of how large the outward movement has been at certain times, particularly during the period of commercial depression which marked the middle nineties. Thus in 1895 while there were 258,536 arrivals of immigrant aliens, there were 216,665 departures of the class mentioned, making a total gain of only 41,871; in 1898 the net gain was only 98,442 against a total immigration of 229,299. Unfortunately, figures are not available for 1896–1897. The importance of this phase of the subject eventually became so evident that in the immigration law of 1907 a provision was included requiring masters of departing vessels to file accurate and detailed lists of their alien passengers, giving certain important facts concerning them. Accordingly, in the fiscal year 1908 we have for the first time complete and accurate data regarding departing aliens.