Page:Popular Science Monthly Volume 3.djvu/408

394 particular case. The author has found that, in general, they are of no practical assistance to the student, and even in some cases [are] confusing."

How an interpolation is to be made unless by the aid of a formula, the author does not tell us, although the mind naturally is anxious upon so important a point.

He goes on to add a practical precept, however, to the effect that he desires to impress upon the student the importance of obtaining the Greenwich time "almost invariably" before consulting the "Almanac." As the "Nautical Almanac" is so constructed that no element can be taken from it without a knowledge of the Greenwich time, it seems almost a work of supererogation to "impress" this fact at the 26th page of a work on navigation.

But, allowing these two practical precepts to stand as examples of the conclusions which the author's experience at sea has led him to, let us briefly notice some of the more important features of the early portions of the treatise, remarking that, to fulfil its purpose as a suitable text-book, these should be exact and clear; and, further, remembering that it is important that the interests of the student should be sedulously guarded, and that his first ideas should be of the most definite nature and strictly correct.

Let us remember, too, that a very poor book, of no peculiar importance in itself, has a claim to notice in an educational point of view. There is hardly a middle ground between goodness and badness in such a one: if it be good, let us have it by all means; if bad, it is a duty to warn others against it.

Perhaps there is nothing more important to the navigator than a clear conception of the astronomical ideas of time, latitude, and longitude. "Longitude," says our author, "is the angular distance between any meridian and a fixed or prime meridian. It may be considered as an angle at the pole," etc.

Longitude of what? Any definition of longitude should begin, "the longitude of a place is," etc. There is no abstract thing called longitude; but there is a certain definite coordinate for every point on the earth's surface, which is the object of the definition. The same objection applies to the definition of latitude.

On page 18 we learn that "time is the hour-angle of some heavenly body, whose apparent diurnal motion is taken as a measure." Now, there is such a thing as time in the abstract, portions of which we measure, or have measured for us, by certain recurring phenomena.

The explanations of apparent time and of the equation of time are equally faulty; but imagine the surprise of the astronomer, who is told that "astronomical time commences at noon, and is measured toward the westward!"

From this, to measuring eternity toward the northeast, is but a step. It is evident that, in the author's mind, the words "time" and "day" were equivalent.

With these fundamental errors in the book, it is scarcely probable that it should not be faulty in other ways. And, indeed, it will be found in many points inaccurate, confused, often unintelligible. Perhaps it is hardly necessary to mention certain other faults of the book, which are still discreditable. Many of its demonstrations are taken directly from other text-books, and in no instance, we believe, is a proper acknowledgment made. Its chapter on the Compass is reprinted, almost verbatim, from a pamphlet published by the Navy Department on the same subject, and, although the author probably meant to do no injustice, no mention is made of this fact in any way.

On the whole, we must set this down as a harmful book, being full of doubtful statements, of confused mathematics and questionable precepts, and one not likely to improve the art of navigation, or the science of nautical astronomy, in any way.

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