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ADDITIONAL NOTES;

ADDRESSED MORE ESPECIALLY TO

PARENTS AND PRECEPTORS,

ов то

THOSE ADVANCED IN SCIENCE.

ADDITIONAL NOTES

REFERRED TO BY FIGURES IN THE TEXT.

Note 1, p. 28.- THE HOROLOGE OF FLORA.

THE HOROLOGE OF FLORA is alluded to by Pliny with his usual felicity of thought and expression. "Dedi tibi herbas horarum indices; et ut ne sole quidem oculos tuos a terra avoces, heliotropium ac lupinum circumaguntur cum illo. Cur etiam altius spectas, ipsumque cœlum scrutaris? Habes ante pedes tuos ecce Vergilias."-Hist. Nat. lib. xviii. c. 27.

Linnæus enumerates forty-six flowers which possess this kind of sensibility. The following are a few of them, with their respective hours of rising and setting, as the Swedish naturalist terms them. He divides them into meteoric flowers, which less accurately observe the hour of unfolding, but are expanded sooner or later, according to the cloudiness, moisture, or pressure of the atmosphere.

2d. Tropical flowers, which open in the morning, and close before evening every day; but the hour of the expanding becomes earlier or later, as the length of the day increases or decreases.

3d. Equinoctial flowers, which serve for the construction of Flora's dial, since they open at a certain and exact hour of the day, and for the most part close at another determinate hour: for instance, the Leontodon Taraxacum, dandelion, opens at 5-6, closes at 8-9; Hieracium Pilosella, mouse-ear hawkweed, opens at 8, closes at 2; Tragopogon pratense, yellow goat's-beard, opens at sunrise, and shuts at noon with such regularity, that the husbandman who adopts it as the signal of dinner-time need not fear to have his pudding too much or too little boiled; Sonchus lavis, smooth sowthistle, opens at 5, closes at 11-12; Lactuca sativa, cultivated lettuce, opens at 7, closes at 10; Tragopogon luteus, yellow

goat's beard, opens at 3-5, closes at 9-10; Lapsana, nipplewort, opens at 5-6, closes at 10-11; Nymphæa alba, white water-lily, opens at 7, closes at 5; Papaver nudicaule, naked poppy, opens at 5, closes at 7; Hemerocallis fulva, tawny day-lily, opens at 5, closes at 7-8; Canvolvulus, opens at 5-6; Malva, mallow, opens at 9-10, closes at 1; Arenaria purpurea, purple sandwort, opens at 9-10, closes at 2-3; Anagallis, pimpernel, opens at 7-8; Portulaca hortensis, garden purslain, opens at 9-10, closes at 11-12; Dianthus prolifer, proliferous pink, opens at 8, closes at 1; Cichoreum, succory, opens at 4-5; Hypocharis, opens at 6-7, closes at 4-5; Crepis, opens at 4-5, closes at 10-11; Picris, opens at 4-5, closes at 12; Calendula Africana, opens at 7, closes at 3-4, &c.

"Thus in each flower and simple bell,
That in our path betrodden lie,
Are sweet remembrancers who tell
How fast the winged moments fly."

In like manner may be formed a calendar of Flora: thus, if we consider the time of putting forth leaves, the honeysuckle protrudes them in the month of January; the gooseberry, currant and elder, in the end of February, or beginning of April; ; the oak and ash in the beginning, or towards the middle of May, &c.

In concluding this note, the author congratulates those whose flower-gardens adjoin their dwellings. How truly has it been said, that the flower-garden near your house inspires very different feelings from the one at a distance! in the former case each flower is a Friend, with whom you hourly hold converse; you trace its growth from the opening bud to the falling blossom, you mark its wants, and the vase of water or the pruning-knife is at hand to supply them; whereas in the distant garden, the flowers, instead of Friends, are only Acquaintances, casually seen, and immediately forgotten, and of whose progress to maturity you have but an occasional and very imperfect knowledge: take care, therefore, if you be a true vofary, to place the shrine of Flora within a reasonable distance of your dwelling.

Note 2, p. 50.-GRAVITY AND CENTRIFUGAL FORCE.

It may, perhaps, be asked how this decrease of weight could have been ascertained; since, if the body under examination decreased in weight, the weight which was op

posed to it in the opposite scale must also have diminished in the same proportion; for instance, that if the lump of lead lost two pounds, the body which served to balance it must also have lost the same weight, and therefore that the different force of gravity could not be detected by such means. It is undoubtedly true that the experiment in question could not have been performed with an ordinary pair of scales, but by using a spiral spring it was easy to compare the force of the lead's gravity at the surface of the earth, and at four miles high, by the relative degree of compression which it sustained in those different situations. We may take this opportunity of observing, that as the force of gravity varies directly as the mass, or quantity of matter, a body weighing a pound on our earth would, if transferred to the sun, weigh 27 pounds; if to Jupiter, 3 1-10 pounds; if to Saturn, 1 1-9; but, if to the moon, not more than three ounces.

With respect to the effect of the centrifugul force as alluded to in the text, it may be here observed, that it has been found by calculation that, at the equator, the diminution of gravity occasioned by the centrifugal force arising from the rotation of the earth, amounts to about the 289th part. But since this number is the square of 17, it follows, that, if our globe turned more than 17 times faster about her axis, or performed the diurnal revolution within the space of 84 minutes, the centrifugal force would predominate over the powers of gravitation, and all the fluid and loose matters would, near the equinoctial boundary, have been projected from the surface. On such a supposition the waters of the ocean must have been drained off, and an impassable zone of sterility interposed between the opposite hemispheres. By a similar calculation, combined with that decreasing force of gravity at great distances from the centre, it may be inferred, that the altitude of our atmosphere could never exceed 26,000 miles. Beyond this limit, the equatorial portion of air would have been shot into indefinite space. If it were possible to fire off a cannon-ball with a velocity of five miles in a second, and the resistance of the air could be taken away, it would for ever wheel round the earth, instead of falling upon it; and supposing the velocity to reach the rate of seven miles in a second, the ball would fly off from the earth, and be never heard of more.

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