ESSA A Y II.

PART T I.

A TREATISE ON THE USE OF THE TERRESTRIAL AND CELESTIAL GLOBES.

OF THE ADVANTAGES OF GLOBES IN GENERAL, FOR ILLUSTRATING THE PRIMARY PRINCIPLES OF ASTRONOMY AND GEOGRAPHY; AND PARTICULARLY OF THE ADVANTAGES OF THE GLOBES, WHEN MOUNTED IN MY FATHER'S MANNER.

UNI

NIVERSAL approbation, the opinion of thofe that excel in fcience, and the experience of those that are learning, all concur to prove that the artificial reprefentations of the earth and heavens, on the terrestrial and celestial globes, are the inftruments the best adapted to convey natural and genuine ideas of aftronomy and geography to young minds.

This fuperiority they derive principally from their form and figure, which communicates a

more juft idea, and a more adequate reprefentation of the earth and heavens, than can be formed from any other figure.

To understand the nature of the projection of either fphere in plano, requires more knowledge of geometry than is generally poffeffed by beginners, it's principles are more reclufe, and the folution of problems by them more obfcure.

The motion of the earth upon it's axis is one of the most important principles both in geography and astronomy; on it the greater part of thẹ phænomena of the vifible world depend: there is no invention that can communicate fo natural a reprefentation of this motion, as that of a terreftrial globe about it's axis. By a celeftial globe, the apparent motion of the heavens is also represented in a natural and fatisfactory manner.

In order to convey clear ideas of the various divifions of the earth, of the fituation of different places, and to obtain an easier folution of problems in geography, it is neceffary to conceive many imaginary circles to be delineated on it's furface, and to understand their relation to each other. Now on a globe these circles have their true form, their interfections and relative poft ons

pofitions are vifible upon the most curfory infpection. But in projections of the sphere in plano, the form of these circles is varied, and their nature changed; they are confequently but ill adapted to convey to young minds the elementary principles of geography.

On a globe, the appearance of the land and water is perfectly natural and continuous, and fitted to convey accurate ideas, and leave permanent impreffions on the moft tender minds; whereas, in planifpheres one-half of the globe is feparated and disjoined from the other; and thofe parts which are contiguous on a globe, are here separated and thrown at a distance from each other. The celeftial globe has the fame fuperiority over projections of the heavens in plano.

The globe exhibits every thing in true proportion, both of figure and fize; while on a planisphere the reverse may often be observed,

Prefuming that thefe reafons fufficiently evince the great advantage of globes over either planispheres or maps, for obtaining the first principles of aftronomical and geographical knowledge, I proceed to point out the pre-eminence of globes mounted in my father's manner, over the comQ 2

mon,

mon, or rather the old and Ptolemaic mode of fitting them up.

The great and increafing fale of the best globes may be looked upon at least as a proof of approbation from numbers; to this I might alfo add, the encouragement they have received from the principal tutors of both our universities, the public fanction of the university of Leyden, the many editions of my father's treatife on their use, and it's tranflation into Dutch, &c. The recom¬ mendation of Meff. Arden, Walker,* Burton, &c. public lecturers in natural philofophy, might alfo be adduced; but leaving thefe confiderations, I fhall proceed to enumerate the reasons which give them, in my opinion, a decided preference over every other kind of mounting.

The earth, by it's diurnal revolution on it's axis, is carried round from weft to caft. To reprefent this real motion of the earth, and to folve problems agreeable thereto, it is neceffary that the globe, in the folution of every problem, hould be moved from WEST TO EAST; and for this purpose, that the divifions on the large brafs

circle

* An Eafy Introduction to Geography, by Mr. Walker.