Imágenes de página
PDF
ePub

1

PREFACE.

THE

he connexion of astronomy with geography is so evident, and both in conjunction so necessary to a liberal education, that no man will be thought to have deserved ill of the republic of letters, who has applied his endeavours to diffuse more universally the knowledge of these useful sciences, or to render the attainment of them easier ; for as no branch of literature can be fully comprehended without them, so there is none which impresses more pleasing ideas on the mind, or affords it a more rational entertainment.

The fifth edition of my father's treatise on the globes being out of print, I was solicited to reprint it *. To obviate several objections to the form in which he had disposed the problems, I was induced to undertake the present work, in which they are arranged in a more methodical manner, and a great number added to them. Such facts are also occasionally introduced, such observations interspersed, and sach relative information communicated, as it is presumed will excite curiosity, and fix attention.

* The first edition appeared in 1706, the third in 1772. A reprintal of this obsolete work was made in 1810, by the brother (D. Adams) of our late author, which he has denominated, The Thirtieth Edition!!!

EDIT.

Having proceeded so far in this work, I found that it was easy to render it subservient to my plan of publishing, from time to time, “ Essays DESCRIBING THE USE OF MATHEMATICAL AND PHILOSOPHICAL INSTRUMENTS ;" for the description of those which have been contrived to smooth the path to the science of astronomy, or to facilitate the practice of the arts depending on it, could no where be introduced with so much propriety, as in a work which treated of its elementary principles.

'To further this design, it was necessary to prefix an introduction to astronomy. This is divided into three parts : in the first, the pupil is supposed to be placed in the sun, the centre of the solar system ; from this situation he considers the motion of the heavenly host, and finds that all is regular and harmonious. In the second part, his attention is directed to the appearances of the planetary bodies, as observed from the earth. It were to be wished, that the tutor would, at this part, exhibit to his pupil the various phenomena in the heavens themselves : by teaching him thus to observe for himself, he would not only raise his curiosity, but so fix the impressions which the objects have made on his mind, that by proper cultivation they would provea fruitful source of useful employment; and he would thereby also gratify that eager desire after novelty, which continually animates young minds, and furnish them with objects on which to exercise their natural activity. In the third part of this introduction, the received, or Copernican system is explained: by this system the various phenomena of the heavens are rationally accounted for; it shews us how to reconcile the real state of things with the fallacies arising from the senses ; and teaches us that the irregularities observable in the motion of the heavenly bodies, are for the most part to be attributed to the situation from which they are observed. Astronomy, in common with other branches of mathematics, while it strengthens the powers of the mind, restrains it from rash presumption, and disposes it to a rational assent.

The principles of the Copernican system are further elucidated in the third Essay; in which the most improved planetarium, lunarium, and tellurian, are described. These instruinents, though less complicated in their construction and less expensive to the purchaser, than those large ones heretofore made for the same purpose, are equally, perhaps better, adapted to explain the general principles of astronomy. In describing them, it was necessary to reconsider many subjects which had been previously treated; but as they are here placed in another point of view, presented to the mind under a different form, are generally described in other words, and often with the addition of new matter, it is hoped that the repetitions, so far from being an object of complaint, will be found to contribute to the main intention of this work, by conveying further instruction, fixing it more deeply in the mind, and rendering that obvious which before might be found difficult.

One part seemed wanting to an introductory treatise on practical astronomy; something that would gently lead the pupil to a knowledge of the practical part of this science, a branch of astronomy to which we are indebted for our present knowledge of the heavens, by which geography has been improved, and by which the passage of ships over the trackless 'ocean is facilitated.

There is no part of mathematical science more simple and easy, than the measurement of the relative positions and distances of inaccessible objects ; yet to the uninstructed, to determine the distance of a ship on the ocean, to ascertain the height of the clouds and meteors that float in the atmosphere, to fix the latitude and longitude of places, &c. are problems that have ever appeared to be above the reach of human art; they are therefore particularly calculated to engage the attention of young minds, and may be used to encourage diligence, and reward application.

To introduce the pupil to this branch of astrono.-my, I have described two instruments, each of which is simple in its construetion, and of small expence. By these he may find the distance of any ipaccessible object, the height of a spire, a mountain, or any other elevation ; learn to plot a field; ascertain the altitude of a cloud, a fire ball, or any other meteor ; determine with accuracy the hourof the day,

[ocr errors][merged small]
« AnteriorContinuar »