the sun's light, and one reflection between them; and the exterior by two refractions, and two sorts of reflections between them, in each drop of water.

Des Cartes, who does not use to betray his tutors, took the hints from Antonius de Dominis, and went on mathematically, and with much demonstration, to give us a theory of the iris, from the laws of refraction, which lucid rays do suffer in passing through diaphanous bodies. He clearly demonstrated the primary iris to be only the sun's image, reflected from the concave surfaces of an innumerable quantity of small spherical drops of falling rain; with this necessary circumstance, that those rays which fell on the objects, parallel to each other, should not after one reflection, and two refractions, (to wit, as going into the drop, and coming out again) be dispersed or made to diverge, but came back again also to the eye, parallel to each other. The secondary iris, he supposes produced by those rays of the sun, which fall more obliquely, but after the same manner as before only in these there are two reflections, before the sun's rays, refracted a second time, and tending towards the eye in a parallel position, can get out from the aqueous globules.

The acute and accurate Mr. Halley comes after the French philosopher, and shows how the Cartesian problems were more easily solved, than the author himself imagined. He shows how to determine the angle, by which the iris is distant from the opposite point of the sun; and the ratio of the refraction being given geometrically, or vice versa, the iris being given, to determine the refractive power of the liquor. And he goes on to cultivate the subject with the ingenuity proper to so accomplished a gentleman.

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But then comes the admirable Sir Isaac Newton, whom we now venture to call the perpetual dictator of the learned world, in the principles of natural philosophy; and than whom, there has not yet shone among mankind a more sagacious reathe laws of nature. This rare person, in his incomparable treatise of Opticks, has explained the phenomena of the rainbow; and has not only shown how the bow is made, but how the colours whereof antiquity made but three, are formed; how the rays do strike our sense with the colours, in the order which is required by their degrees of refrangibility, in the progress from the inside of the bow to the outside the violet, the indigo, the blue, the green, the yellow, the orange, and the red.

In a book entitled, Thaumantiadis Thaumasia, published at Norimberg, the skilful author lays together whatever is to be found upon this argument, among the modern, as well as the ancient writers.

It is good advice given by the son of Sirach; look upon the rainbow, and praise Him that made it. Frytschius says:

"When you discern the bow of heaven to rise,
The brightest meteor there salutes your eyes:
Producing various colours on the cloud,

Mankind behold it, and survives the flood.
Behold it, sirs, a sign of heavenly love,
And of a covenant made by God above:
Almighty God did by that sign engage
To keep his Noah's world from age to age.
'Tis thus engaged, God will no more employ
Deep waters, as of old, men to destroy."

The halo is of so near kindred to the rainbow, that it claims a mention with it: a circle that surrounds the sun, or the moon, or a star, is sometimes coloured like a rainbow. According to Sir

Isaac Newton, it arises from the sun's or moon's shining through a thin cloud, consisting of globules of hail or water, all of the same size. Mr. Huygens conceives it formed by small round grains of a kind of hail, made up of two parts; one of which is opaque, and inclosed in the other, which is transparent. The same way he accounts for the parhelia. Only there he apprehends, that the icy grains are of an oblong figure, and rounding at the ends like cylinders, with round convex tops. May we look upon the rainbow, and praise Him that made it! My readers, will you give me leave to teach you the use of the bow? Mercer tells us, the religious Jews in many places, upon the appearance of a rainbow, go forth and fall down, and confess their sins, and own themselves worthy to be drowned with a flood for them. To us Christians, our Lord says, what do you more than they?"As the sight of the rainbow should bring to remembrance, what a woeful, what a fearful desolation, once came upon a wicked world, whose foundation was overflown with a flood! So the sacramental importance, now instamped by the will of God upon the rainbow, should be ac knowledged with us. It should be considered as a sign and a seal of a covenant, which the great God has made, that He will not have this world, though a sinful one, drowned any more, nor his church in the world. Upon the view of the admirable meteor, how proper this doxology; Blessed be our gracious, merciful, and long suffering Lord; who hath sworn, that the waters of Noah shall go over the earth no more! But then, how can we forget the glorious Christ, who is our head in the covenant; and about whose

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head there has been the appearance of a rainbow, in the visions of his prophets, betokening our dependence upon Him for all our preservations! But then we are not excused from, but rather excited to these further thoughts on this occasion: That though a watery flood, which may drown the world, is no more to be feared; yet there is a fiery flood, for the depredations whereof, a mise-rable world is growing horribly combustible.

ESSAY XIV. Of SNOW.

Of snow there are many curiosities observed by the excellent Dr. Grew.

He observes, as well as Des Cartes, and Dr. Hook, that very many parts of the snow are of a most regular figure; they are generally so many rowels, or stars of six points, being as real, as perfect, as transparent ice, as any one may see upon a vessel of water: on each of which six points, there are set other collateral points, and those always at the same angles as are the main points themselves. These are of divers magnitudes; many are large and fair, but some are very minute.

Among these, there are found some irregular ones, which are but fragments of the regular. But some seem to have lost their original regularity, not by being broken, but by various winds, first gently thawed, and then froze into such irregular clumpers again. A snowy cloud seems then to be an infinite mass of icicles regularly figured, not so much as one of the many millions being irregular. A cloud of vapours is gathered into drops; the drops forthwith descend. On the descent they pass through a soft wind that freezes them,

or a cold region of the air, by which each drop is immediately froze into an icicle, that shoots forth into several points from the centre. But still continuing their descent, and meeting with some sprinkling little gales of a warmer air, or in their continual motion or waftage to and fro, touching upon each other; some are a little thawed, blunted, frosted, clumpered; others broken: but the most hanked and clung in several parcels together, which we call flakes of snow.

It should seem, that every drop of rain contains in it some spirituous particles. These meeting in the descent, with others of an acido-salinous nature, the spirituous parts are apprehended by them, and with those the watery; and so the whole drop is fixed, but still according to the energy of the spirituous, as the pencil, and the. determinate possibility of the saline parts, as a ruler, into a little star.

Though the snow seem soft, yet it is truly hard; it is ice; but the softness of it is from this ; upon the first touch of the finger on the sharp edges, it thaws immediately; the points would else pierce the fingers like so many lancets.

Again, though the snow be true ice, and so hard and so dense a body, yet it is very light: this is because of the extreme thinness of each icicle, in comparison of the breadth. As Gold, though the most ponderous of all bodies, beaten into leaves, rides on the least breath of air.

"When we see the snow, that comes down from heaven, and returns not thither, but waters the earth, and makes it bring forth and bud; we cannot but hope, that the word of our God, which comes like it, will continue with us, and accomplish the intentions of it.