Gardeners Dictionary: Rainbow

Gardeners Dictionary:
containing The Best and Newest Methods of Cultivating and Improving The Kitchen, Fruit, Flower Garden, and Nursery; As also for Performing the Practical Parts of Agriculture: Including The Management of Vineyards, With the Methods of Making and Preserving Wine, According to the present Practice of The most skilful Vignerons in the several Wine Countries in Europe.

Together with Directions for propagating and improving, From real Practice and Experience, All sorts of Timber Trees.

The Eight Edition,
Revised and Altered according to the latest System of Botany; and Embellished with several Copper-Plates, which were not in some former Editions.

By Philip Miller, F. R. S.
Gardener tothe Worshipdul Company of Apothecaries, at their Botanic Garden in Chelsea, and Member of the Botanic Academy at Florence.

London,
Printed for the Author;
M. DCC. LXVIII.

(Lontoo 1768)

RAINBOW, a meteor in form of a particoloured arch or semicircle, exhibited in a rainy sky opposite the sun, by the rarefaction of his rays in the drops of falling rain.

The Rainbow, Sir Isaac Newton observes, never appears but where it rains in the sunshine, and may be represented artificially by contriving water to fall in little drops like rain, through which the sun shining exhibits a bow to the spectator's eye placed between the sun and the drops, especially if a dark body, e. g. a black cloth be disposed beyond the drops.

Anton. de Dominis first acoounted for the Rainbow in 1611, he explained at large how it was formed by refraction and reflexion of the sun-beams in spherical drops of water, and confirmed his explication by experiments made with glass globes, &c. full of water, wherein he was followed by Des Cartes, who mentioned and improved upon the account.

But as they were both in the dark as to the true origin of colours, their explications are defective, and in some things erroneous, which, it it is one of the glories of the Newtonian doctrine of colours, to supply and correct.

The folloring properties are ascribed to the Rainbow:

1. That it never appears but in a place opposite the sun; so that, when we look directly at it, the sun is always behind us.

2. That when the Rainbow appears, it always rains somewhere.

3. That hte constant order of the colours is, that the outmost is red or Saffron colour; the next is yellow; the third is green; the fourth or inmost is Violet or blue; but these colour are not equally bright.

4. Two Rainbows appear together, one of which is higher and larger than the other, and shews the aforesaid colours, but in an inverted order.

5. The Rainbow is always exactly round, but does not always appear equally entire, the upper or lower parts being very often wanting.

6. Its apparent breadth is always the same.

7. That those, who stand upon plain low ground, never see above half its circle, and oftentimes not so much.

8. The higher the sun is above the horizon, the less of the circle is seen, and, if there be no cloud to hinder, the lower, the more of it.

9. That never any Rainbow appears, when the sun is above 41 degrees 46 minutes high.

Lunar (Rainbow:) The moon also sometimes exhibits the phænomena of an iris or bow by the refraction of her rays in the drops of rain in the night time.

Aristotle says, he was the first that ever observed it; and adds, that it never happens, i. e. visible, but at the time of the full moon, her light at other times being too faint to reflect the sight. After two refractions and one reflecion, the lunar iris has all the colours of the solar very distinct and pleasant, only faint, in comparison of the other, both from the different intensity of the rays, and the different disposition of the medium.

Marine (Rainbow) is a phænomenon sometimes observed in a much agitated sea, when the wind, sweeping part of the tops of the waves, carries them aloft, so that the sun's rays falling upon them, are refracted, &c., as in a common shower, and paint the colours of the bow.

F. Bourzes, in the Philosophical Transactions, observes that the colours of the Marine Rainbow are less lively, distinct, and of less duration, than those of the common bow; that there are scarce above two colours distinguishable, a dark yellow on the side next the sun, and a pale green on the opposite side. But these bows exceed as to number, there being sometimes twenty or thirty seen together; they appear at noon-day, and in a position opposite to that of the common bow, i. e. the concave side is turned upwards, as indeed it is necessary it should be, from what may be said in accounting for the appearance of the solar bow.