occasionally introduced, such observations interspersed, and such relative information communicated, as it is presumed will excite curiosity, and fix attention.

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 prove a 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 instruments, 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 astronomy, I have described two instruments, each of which is simple in its construction, and of small expence. By these he may find the distance of any inaccessible 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 hour of the day,

the latitude or longitude of a place, with many other curious problems. In the selection of these, for the first edition, I have to acknowledge the assistance I received from an ingenious friend.

The Editor to this sixth edition, thinks it necessary to inform the Reader, that this work has been again carefully revised by him, all observed errors corrected, new astronomical discoveries inserted, including a plate of the path and descriptions of the two, recent very remarkable comets, and such other additions made, as appeared necessary to the information of the beginner, and the use of the preceptor.

On the decease of our worthy author, some years back, his widow, not meeting with a liberal and adequate offer, either by private treaty, or public auction, for the copy-rights of her husband's valuable works; on her application to the Editor and his Brother, by an advanced tender, they became, impartially, the purchasers. This explanation, will prevent the effect of an unjust insinuation or misrepresentation. It is hoped, that the Editor, without the imputation of arrogance to himself, may add, that the works have been rendered the most correct in his own department, by thus coming under his attention and revision.

Holborn, August 1, 1812.

NEW BRITISH GLOBES.

W. and S. JONES think it proper hereby to inform the reader, that there are now completed two entire new sets of engraved plates, for Globes of eighteen and twelve inches diameter. The many recent geographical and astronomical discoveries have rendered the old globes inaccurate and obsolete, and new ones indispensably

necessary.

On the 18-inch Terrestrial, are inserted all the lastest discoveries from the voyages of Capt. Cook, Vancouvre, Perouse, &c. engraved from an accurate drawing by Mr. Arrowsmith, and all the names of the places delineated in a clear and distinct manner. On the Celestial, is depicted the exact places of more than 6000 stars, clusters, planetary, nebulæ, &c. communicated by Dr. Herschel and other astronomers, and calculated, in position, for the present century, or the year 1800, by W. Jones. The size of these Globes, which is considered of the dimensions the most manageable, renders them comprehensive of many particulars not to be contained in smaller ones. The graduation of the great circles are to 20 minutes of a degree; and by simple and improved hour circles, the time is shewn to a few minutes. The Globes are so constructed, as in the simplest manner to be capable of all solutions that it is possible for globes to give, and the names are in the English language.

The general prices, per pair, are from 8 to 18 guineas, according to the frames, mounting, &c. as may be seen in W. and S. Jones's Catalogue of instruments annexed.

The 12-inch Globes are reduced copies of the above 18-inch, and contain rather more than half the countries, stars, &c. that are upon the 18-inches. The graduations of the great circle are to 30 minutes, or half a degree,

The price in plain frames, the pair, is 4 guineas, and 5 shillings for the addition of a compass fitted to both horizons of the Globes. In mahogany claw-feet frames, 6 guineas.

• The Globes may be packed securely in packing cases, so as to be conveyed safely to all parts of the world.