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Fuft as the Spirit of Love is fent abroad,
Warm thro' the vital Air, and on their Hearts
Harmonious feizes, the gay Troops begin,
In gallant Thought, to plume the painted wing;
And try again the long-forgotten Strain.
At first, faint warbled, but no fooner grows
The foft Infufion prevalent and wide,
Than, all alive, at once their Joy o'er flows
In Mufick unconfin'd. Up Springs the Lark,
Shrill-voic'd, and loud, the Meffenger of Morn;
Ere yet the Shadows fly, he mounted fings
Amid the dawning Clouds, and from their Haunts
Calls up the tuneful Nations. Every Copfe
Deep-tangled, Tree irregular, and Bufh
Bending with dewy Moisture, o'er the Heads
Of the coy Choristers that lodge within,
Are prodigal of Harmony.

It would be tedious to purfue him thro' all his fine Reflections on the vernal Seafon, and its agreeable and beneficent Effects on all the World.I fear I have tired your Patience already; but, my dear Euphrofyne, I know you'll forgive a Digreffion of this Kind, were it much longer, in Complaifance to the Muses.

Euphrof. I hear you with equal Patience and Pleafure. This happy Seafon can't be too much extolled,

-But, fee, the Earth is moved far on; the Spring begins to give Way to Summer, which I fuppofe will here fucceed, as it does in Nature.

Cleon. In the very fame Manner. As the Middle of the Spring Seafon is about the 20th of March, when the Sun (S) appears in the Beginning of Aries (r); fo about the Beginning of May, the Spring ends, and the Summer Seafon commences, which we will next contemplate on the Orrery.

TH

DIALOGUE X.

Of SUMMER.

Euphrofyne.

HE Earth being near advanced to Capricorn (v), shews the Serenity of Spring is paft, and the near Approach of Summer. But fince the Earth is ftill at the fame Distance from the Body of the Sun, I can't rightly conceive how it comes to pafs, that the Sun-beams are so much hotter than at other Times.

Cleon. To explain that, is one great Defign of the Orrery. In order to which, you must confider, and understand, that the principal Characteristics of Summer are two, viz. (1.) The Days are then longeft; and (2.) The Heat is most intenfe. How the Days are now longest, I fhall explain to you at large, after we have done with the Seafons. I fhall now only fhew you why the Heat is greater with us than at any other Time of the Year.

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Euphrof. Why do you fay, with us, fo emphatically, Cleonicus?

Cleon. Because with refpect to the Earth in general, the Sun's Heat is nearly always the fame; but greater or leffer only in regard of fome particular Place at fome certain Seafons of the Year, as with us when the Sun appears in Cancer (); for at that very Time it is coldest in some other Part of the Earth.

Euphrof. But what I want to know is, how it comes to pass, that it is fometimes very hot, and fometimes very cold at different Times of the Year in the fame Place?

Cleon. The Reafon of that will eafily be understood, if you remember what I obferved to you about the Axis of the Earth (N S) not being perpendicular to the Plane of the Ecliptic (or) but inclined thereto; and alfo, that the Earth fo moves as always to have its Axis parallel to itself, or pointing to the fame Part of the Heavens.

Euphrof. I remember that very well, and-now I look on the Earth, I readily fee what follows, viz. the

North

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North Pole (N), by this Inclination of its Axis, is carried more and more towards the Sun, as it arrives nearer and nearer to the Beginning of Capricorn (). —

Cleon. Very good, my Euphrofyne; and when it comes there, you will obferve, that all the Places of the Earth which have North Latitude are turned more directly towards the Sun than when in its first Position in the Spring. And, confequently, the more directly the Sun's Rays fall on any Part, the thicker or denser they will be, and therefore, fo much the hotter. Thus, for

Example, fuppofe a Parcel of Rays, abc d, fall directly, or perpendicularly on any Plane, A B, and obliquely on another Plane, A C, 'tis evident, they will take up a fmaller Space, cd, in the former, than ef, in the latter; and fo their Action, i. e. their Heat would be much greater in the leffer Space cd, than in the larger ef; and if, instead of Lines, we fuppofe cd and ef to be the Diameters of Surfaces, then the Heat on those Surfaces will be inverfely as the Squares of the Diameter, viz. as the Square of ef to the Square of cd. And this would be the Cafe with respect to the Inhabitants of the Earth, if we were to regard the Sun's Rays only; but, as I faid, the greater Length of Day contributes to augment the Heat: And moreover, another Reason which I have not before mentioned, is, that the Rays do now pass through a far lefs Portion of the Atmosphere, and therefore, are not fo much refracted and weakened by it, as when they fall more obliquely on the Earth, and so pass thro' a greater Part of it.

Euphrof. When you talk of the Atmosphere, you go a little out of my Depth, Cleonicus; pray, explain that a little farther to me.

Cleon. I will. The Earth is furrounded on all Parts by a Body of Air of a spherical Form to a certain Height (which I have reprefented by the dotted Circumference about the Figure of the Earth in this little Scheme, for Illuftration Sake) this Body of Air being filled with watry, &c. Particles, exhaled from the Earth, occafions the Sun's Rays, in paffing thro' it, to be variously refracted, and blended thro' its Subftance, and the more fo, the more obliquely they are received by it; and confequently, the more their Action or Effect is weakened and abated on the Surface of the Earth.

Euphrof. Pray give me an Example of this, Cleonicus; I fhal then better apprehend you.

Cleor. You fee the Earth is now just arrived to the firft Scruple of Capricorn () where it has the same Pofition, with Regard to the Sun, as the Figure thereof has in this Scheme. At this Time the Days are longeft, and the Sun's Rays fall more direct upon us, and therefore are strongest in their immediate Effects, and therefore, this is the Middle of Summer, which you fee happens about the 11th of June; for against that Day the Earth now ftands in the Orrery.

Euphrof. I fee it does; and had you not better ftop it there for fome Time?

Cleon. Yes, I intend it. Obferve, in the Scheme, the Situation of the City of London L, the Pofition of the Earth, you fee, at this Time turns all the Northern Hemisphere (QN Æ) as much towards the Sun as they can be, and more than at any other Time of the Year; and confequently, the Sun's Rays fall on this Metropolis, at this Time, more directly than at any other; and their Paffage thro' the Atmosphere (O L) the fhorteft of all. And therefore all Things 'confpire to make this the warmeft, and most lightsome Season of the Year with us.

Euphrof. You have made the Matter fo plain, that I fhould be dull not to underftand it tolerably well.And I further obferve, that in this Position of the Earth, all the Southern Hemisphere (QS ) is turned as much away from the Sun as can be; and fo, I prefume, it must be Winter with all those who live in Southern Latitude, at this prefent Time.

Cleon. You judge very right; for fuppofe the Place M hath its South Latitude QM equal to the North Latitude of London QL; the Days will there be the shorteft, the Sun's Rays will fall on it most obliquely, and their Paffage thro' the Atmosphere (X M) will then be greatest of all; and confequently, every Thing there combines to make it the coldest Season of the Year; i, e. their Winter; all which is, I think, evident from the Scheme.

Euphrof. It is fo; and I never confidered 'till now, that when it is Summer in ene Part of the Earth, it is