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Page:Popular Science Monthly Volume 7.djvu/442

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Rightly interpreted and followed out, these aerial echoes lead to a solution which penetrates and reconciles the phenomena from beginning to end. On this point I would stake the issue of the whole inquiry, and to this point I would, with special earnestness, direct the attention of the Lighthouse Board of Washington. Let them prolong their observations into calm weather: if their atmosphere resemble ours—which I cannot doubt—then I affirm that they will infallibly find the echoes strong on days when all thought of reflexion "from the crests and slopes of the waves" must be discarded. The echoes afford the easiest access to the core of this question, and it is for this reason that I dwell upon them thus emphatically. It requires no refined skill or profound knowledge to master the conditions of their production; and, these once mastered, the Lighthouse Board of Washington will find themselves in the real current of the phenomena, outside of which—I say it with respect—they are now vainly speculating. The acoustic deportment of the atmosphere in haze, fog, sleet, snow, rain, and hail, will be no longer a mystery: even those "abnormal phenomena" which are now referred to an imaginary cause, or reserved for future investigation, will be found to fall naturally into place, as illustrations of a principle as simple as it is universal.


While this Preface was passing through the press, the intelligence of the loss of the Schiller thrilled through the land. 1 look forward to a time when such a calamity upon our coast will be a simple impossibility. It is in our power to make it so; and that power will, I doubt not, be promptly and wisely employed.

Royal Institution, May, 1875.




IN the construction of new charts for the use of navigators, as well as in the correction of old ones, the assignment of different latitudes and longitudes to the same point, by various authorities, has always been a source of difficulty and embarrassment.

The exact position of all prominent points on the coasts of the United States, as well as those of England, France, and other European nations, has been determined with great accuracy; but a large portion of the earth's surface is still very imperfectly and inaccurately laid down on marine charts.

The latitude of any point being determined directly by observation, and independently of the latitude of any other place, is less likely to be in error than the longitude, which can only be ascertained with