In the current issue of the SUPPLEMENT will be found an article by Prof. Heilprin, entitled The Shrinkage of Lake Nicaragua, which is certainly the most significant, we had almost said dramatic, contribution to the literature of the Nicaraguan region that has yet appeared, In our issue of February 24, the same author, whose geographical and geological attainments give him eminent authority, showed that there is abundant evidence, drawn from the inconsistency of early recorded levels with those of later surveys, and from other phenomena, that there has been a gradual falling of the lake level. A reply to this article by Mr. C. Wil-lard Hayes, geologist of the Walker Canal Commission, was published in the SUPPLEMENT of April 28, and in the present article, while replying to Mr. Hayes, Prof. Heliprin fortifies the position taken in his former article, by proving from the records of rainfall, evaporation and outflow of the lake, furnished in the report of the Walker Commission of 1897-99, that there has been a shrinkage in the waters of the lake during the past twenty years. It is evident that, if any doubt exists as to the permanence of the lake, a similar doubt exists as to the permanence of the canal; for not Nicaragua, with the canalized San Juan River, to form the major portion of the canal, but it is upon the maintenance of the lake at or above a certain specified minimum level that the very existence of the whole system depends. Should the waters of the lake in time fall below a level which would afford less than 30 feet (the proposed depth of the canal) at the points where the canal enters and leaves the lake, there would be absolutely no remedy for the disaster. Does such a danger exist ? Is there any evidence that the average losses by evaporation and outflow are in excess of the average gains by rainfall in the Nicaragua watershed ? The question can be answered by gathering all the recordeddata on the subject, and by a simple process of addition and subtraction, determining whether the volume of the lake is increasing, stationary or undergoing a steady shrinkage. The necessary data are furnished by careful records taken at-Rivas, on the Pacific side of the lake, during the years 1880 to 1898 inclusive, and it is from these data that Prof. Heilprin has arrived at the discouraging -conclusion that the lake--unless, indeed, the official reports are inaccurate--has been steadilyand progressively undergoing shrinkage, anti.that it must continue to do so in the future.. The determinations of altitude of the lake made by Galisteo, in 1871, and by Baily, in 1838, show that it formerly stood at a much higher level than that established by recent surveys, a fact which is confirmed by the report of Collinson to the Royal Geographical Society, in 1867, who states that even the least observant native, dwelling on the lake, will tell how its banks are rising year by year visibly before his eyes. The most comprehensive record of rainfall, evaporation, etc:, is that contained in the report of the Nicaragua Canal Commission of. 1897-99, which, although it makes no specific analysis of its own figures to determine the question of net gain or loss in the volume of the lake, does actually afford . confirmation of the statements of the early engineers, as Prof. Heilprin shows in his article. It is made plain from the report that the intake of Lake Nicaragua--rainfall and drainage from its drainage basin;--is apparently for almost every -year less than the output--the loss due to evaporation and outflow ; while in exceptionally dry years the evaporation alone is greater than the entire intake. From November 1, 1889, to June 1, 1891, the total rainfall would have raised the level of the lake 45;75 inches. The evaporation alone would have lowered it 95 inches, a loss, outside of what would have run off through the San Juan River, of rover 4 feet. The aggregate loss during three dry spells, not taking count of outflow through the San Juan, was 10 feet 10 inches. The compensations for such losses must be found in periods of extraordinarily heavy rainfall; but despite the.fact that immediately after excessive rains the lake has been known to rise two feet in six weeks, the great-estfiaet accession-to the lake for any entire year, during a period of 20 years, was considerably less than 2 feet. In the, year 1898, when the rainfall was 108 inches, the net rise of th lake was .only 18 inches, and a comparison, of the records show that durjng 19 years of successive observations (1880 to 1898) there were not more than four, periods, the years 1893, 1897, 1898 and possibly 1886, when the lake held, its own, and during these years combined the actual gains were less, .than 5 feet. On the other hand, irr th single year 1890, when the rainfall at Rivas was only 3181 inches, the loss was as great as the gains for the entire 19 years In calculating the net result of all the causes of supply and loss affecting the lake level, the average recorded evaporation is taken as 55 inches, and the outflow through the San Juan as 42 inches, or one-half the amount in the extremely wet season of 1898. On this basis there is a total loss of 363 inches as against a total gain of 114 inches, or a net loss of 20 feet 9 inches. From this result the author of the paper concludes that for a long period of years Nicaragua has undergone a very marked and progressive shrinkage. It is true that the outflow through the San Juan maybe controlled and water may be stored in wet seasons against the deficiencies due to drought ; but although the evil day may be thus postponed it is only a question of time, if the lake be steadily shrinking, when the surplus storage will be inadequate to meet the ever-growing deficiency. We agree -with the author of this paper that it is hardly less than amazing that these reports should not have been analyzed before, and their bearing given full consideration ; and, we trust, that Congress will recognize, in the grave considerations thus presented, a further inducement to await the results of the searching investigation which is now being made by the Presidents commission.